Manchester United's failed attempt to sign Ander Herrera is not the only time the Premier League champions have experienced bizarre tactics at the top end of the market during a difficult, complicated transfer window that has brought fierce criticism on the club.

United's information is that earlier this summer a forged email, purporting to originate from Old Trafford and reputedly confirming their interest in a player, was sent to another club in an apparent attempt to trigger a rival bid and increase the price. That player has subsequently moved, for significant money, with the buying club under the false impression they were beating United to him.

The revelation is an insight into some of the tricks employed by clubs, agents and other middle men when such vast sums of money are swilling around before the transfer deadline. However, it is the Herrera deal that has caused the most consternation behind the scenes at Old Trafford and, specifically, the role of the three lawyers who turned up at the offices of the Spanish league (the LFP) on Monday apparently purporting to have United's authorisation to sign off the €36m (£30.4m) buyout clause.

The club are aware that journalists have been briefed by sources at the Spanish league that the three men – identified as Rodrigo García Lucas, Alvaro Reig Gurrea and Guillermo Gutiérrez, from the Spanish law firm Laffer – were, in fact, operating officially on United's behalf.

United's position is that surely the only confirmation of this should come from Old Trafford and they have reiterated, categorically, that they did not know of these men, recognise them or commission them.

United employ their own legal firm in Spain but did not mobilise it for one simple reason: no agreement was reached with Athletic Bilbao and they never had any intention of paying the full price when they valued Herrera £10m lower.

Instead, the arrival of Laffer's lawyers – credited with helping to arrange Javi Martínez's transfer from Bilbao to Bayern Munich a year ago – created the impression the deal was imminent and led to a frenzy of speculation; the Bilbao newspaper El Correo compared the pursuit of Herrera to a Benny Hill sketch.

United's version is rather more straightforward. Having followed Herrera for two years, they had concluded he was worth around £20m, their feeling being it would be another 18 months or so before he was a guaranteed first-team pick. Bilbao insisted they wanted the full amount, no compromise was reached and that would have been it finished, in United's opinion, until the television pictures of Laffer's representatives led to the inaccurate impression that an agreement was close – building up hopes for a deal that had already failed. The Guardian on Tuesday night contacted the law firm Laffer who, for reasons of professional confidentiality, declined to comment or to reveal the identity of their client.

Two days on, there is still confusion at Old Trafford about the involvement of the three lawyers described on deadline night as "impostors" and United feel so strongly about it they have been willing to put their position on the record. Herrera has also, to a point, backed their story. "I do not feel used by United. How can I feel used? They made a formal offer. Athletic did not want to negotiate, I value that. They [United] had to pay the €36m clause. I reached no agreement with United. I am proud they made an offer for me, and that Athletic wanted me [to stay]."

Manchester United's failure to sign Ander Herrera from Athletic Bilbao has caused consternation at Old Trafford. Photograph: AFP/Getty Images

Herrera's agent has been in touch with United to ascertain if they knew who the lawyers were. United's response was emphatically no. Herrera added: "The lawyers that were at the LFP did not represent me. I didn't even know who they were."

It is a confusing, complex and embarrassing issue for United, even if it is true it was not a farce of their own making. What is beyond dispute is that they have found the transfer window frustrating and unsatisfactory. They are, however, a lot more relaxed about it than might be expected and bemused, too, about some of the mistruths that have accompanied the genuine disappointments.

United are taken aback, for example, by the latest suggestion they challenged Arsenal for Mesut Ozil. The truth is that United and Manchester City were both offered the player three weeks ago. United turned it down because they had already made up their mind that Wayne Rooney would not be leaving and they did not want to break their transfer record, paying upwards of £40m, for someone who plays in the same position.

Their thinking also took into account they have Shinji Kagawa, among others, for the No10 role. Kagawa still features prominently in the thinking of David Moyes despite not even being on the bench against Liverpool on Sunday. His problem is two-fold: one, that he has had an exhausting summer with his national team and is being brought back slowly; two, that Moyes has not really seen him play or got to know him very well. He is not, however, being marginalised.

United rebuffed an approach from Atlético Madrid for the Japan international and would have done the same if Borussia Dortmund had been in touch. As it was, there has not been a single telephone call from the Bundesliga club, despite talking up a possible return.

Juan Mata is a player United like but linking the Chelsea midfielder with a move to Old Trafford was, like Ozil, a red herring. Mata, as Chelsea have repeatedly stated, was not for sale; it is just that some people did not believe them. United did not try to get him and he was never mooted in a cash-plus-player exchange with Rooney because, as the Guardian revealed last month, Rooney was never going to be allowed to join Chelsea, no matter what the offer. Behind the scenes at Old Trafford, there is frustration that this has largely been overlooked when it has taken up so much time and effort and, in their opinion, could be the difference between United winning the title or not.

Rooney's determination to force a transfer, with a proactive agent in Paul Stretford, and Chelsea doing everything they could to push it has been such a major issue at Old Trafford it is estimated to have taken up more than half the time that United's top-level officials have devoted to working on player arrivals and departures. United were determined to make a show of force and efforts are continuing behind the scenes to convince Rooney that he can, once again, be happy at Old Trafford. It is a continuing process and there is an acceptance it will not be easy. However, it is being seen as a victory of sorts that they refused to cave in, as a point of principle, when the alternative was potentially to see him scoring 20 goals a season at Chelsea for the next few years.

That still leaves a lot of unanswered questions such as why United paid £27.5m for Marouane Fellaini when his buyout clause could have been activated earlier in the summer for £4m less. The long pursuit of Cesc Fábregas was fundamentally flawed because they were encouraged to believe he was open to the offer; United, in short, were told Fábregas was increasingly agitated about his potential lack of games for Barcelona in a World Cup year – but ultimately they could not get the man they regarded as their top target and they recognise that amounts to a long, drawn-out failure.

The issue of Thiago Alcântara also needs clearing up. In his case, it has been portrayed as him snubbing United for Bayern Munich when the truth is actually that Moyes decided he was not entirely comfortable going for the Barcelona player. United had been monitoring him for three years and effectively lined up the transfer but Moyes, as everyone at Everton can testify, likes to have a huge amount of background information on new signings and, having initially gone along with it, decided in the end he did not want to take someone else's word about a player he had seen infrequently. Again, it boils down to a new manager shopping in a new market, with a limited amount of time.

United had not wanted to overrule Moyes and promised they would keep their squad together, with the exception of Bébé. They have kept true to that and, as well as rejecting the approach for Kagawa, they turned down a Tottenham offer for Javier Hernández and at least five approaches from different clubs for Nani.

That, nonetheless, does not change the fact Moyes had wanted two central midfielders as well as a rival left-back to Patrice Evra, missing out on Leighton Baines and then Fábio Coentrão. On that basis, there is a frank admission at Old Trafford that they have come up short by bringing in only Fellaini.

United, however, are angry about the suggestion, emanating from the Herrera farce, that a club of their stature and transfer experience somehow failed to understand the Spanish tax system – and bewildered, more than anything, that they are supposed to have employed three lawyers they say they had never heard of.