They are the 21st-century version of pawnbrokers. Barely a TV ad break goes by without a blaring voice offering cash for viewers' DVDs, games, CDs, gold, mobile phones or computers.

The recession has led to a boom in websites offering to buy unwanted jewellery and electronics. There are now so many "recycling" websites that web comparison services have been launched to help consumers find the best price.

But question marks exist over whether consumers are getting a good price, the speed and level of service they receive, and which firms are reputable. In almost every category, consumers can sell their goods for greater sums on eBay than the prices quoted by recycling websites.

The Trading Standards Institute (TSI) has warned that the quotes offered on most goods do not represent good value. "It's more about convenience for most people," the TSI's Sylvia Rook said. "It's often easier to send off a phone and get a cheque in the post than it is to haggle at a pawnbroker or list the phone on eBay. Also, for many people these websites help them avoid the stigma of, say, taking an heirloom to a jeweller in their local area, where someone might see them.

"Whilst the majority of these companies offer a good service, we are aware that some people are not happy with the amount they have been offered for their items. Others have been informed that the item that was in perfect condition when they sent it is now damaged or faulty and therefore worth less than was offered online, and some simply never hear from the company once they have sent the items. Also, some items get 'lost in the post'."

To cash in their goods, users tell the relevant website what they want to sell and are given a quote before sending the item off and waiting for a cheque. But consumers can experience problems with items going missing and quotes being lowered once their item is received.

A year ago the Office of Fair Trading (OFT) asked gold-buying websites to provide information on their business practices and to explain claims made in their ads and on their websites. Among the OFT's concerns was whether consumers' rights to reject offers and get their gold back were being honoured in all cases. The OFT has yet to report its findings, but an update is expected early this year.

The TSI said it had few guidelines for identifying a reputable website and admitted that it was something of a lottery. "The problem is that there are so many of them now," said Rook. "We would advise consumers to research carefully before they send their items to a company for money. Don't just send the item to the company who is offering the most money, but look at customer feedback on the internet to see if people have had any problems with the company you intend to use.

"Send any valuable items by special delivery – if you use standard post, or recorded delivery, the maximum compensation you can receive from the Royal Mail if your item is lost or damaged is 100 times the value of a first-class stamp" (currently £41).

If consumers are not happy with the quote that the company gives them, "don't accept their offer, and ask them to return your goods to you", she said, adding: "You could then consider selling to a different company or, alternatively, selling your item privately through the classified ads or an internet auction site."

DVDs/games/CDs



WeBuyDVDs.co.uk and MusicMagpie.co.uk are two big buyers of games, DVDs and CDs. Both highlight the recycling aspect to their services – which is just as well, given the low prices they pay.

WeBuyDVDs offered £3.89 for the final season of the TV series 24, and Music Magpie £3. Speedsell.co.uk, which buys everything from PCs and phones to toys and jewellery, offered £1.65. In contrast, the box set, which retails for £33.99 at HMV, fetches about £22-£26 on eBay. This means the DVD-buying websites are paying about 90% less than eBay. CDs do not fare much better, with James Rhodes's Bullets & Lullabies taken off your hands by WeBuyDVDs for just £1.29 or £2.31 with Music Magpie, and £10.49-£13.49 at eBay.

Are cash-for-goods websites worth their weight in gold? Photograph: Graphic

Mobiles



Users of the mobile phone-buying sites also face lower quotes than they would get at eBay, although its phone section can be prone to mis-selling, non-payers and time-wasters. Consumers might also find they get better value if they sell their phone back to their current provider or use it to get money off an upgrade.

A working Apple iPhone 3GS 16GB fetches £211 with Mobile Phone Xchange, £200 with Mazuma Mobile, £200 with Envirofone and £190 with WeBuyAnyPhone.com. Users will be offered more if they accept vouchers for retailers such as Debenhams and Argos instead of cash.

O 2 and 3 both offer £200 for the iPhone 3GS, while Orange offers £180, and Virgin Mobile will pay up to £150 in free airtime if you cash in your old phone. Royal Mail's Simply Drop recycling service proves poor value at £175, while Boots Recycle offered £200 worth of Advantage card points. A similar iPhone recently sold for £340 on eBay.

Several mobile phone sales comparison sites have launched to help consumers find the best price for their mobile, but these are hit and miss. The best prices at Sellmymobile.com reverted to lower quotes on clicking through to the actual vendor, meaning you are arguably better off doing your own research.

Gold

The likes of Cash4Gold, Cash Your Gold Now and CashMyGold, which buy gold, silver, platinum and diamond jewellery, have long been a controversial presence in our newspapers and on our televisions. But gold-buying sites face accusations that they pay well below the market rate (10% of the rate in some cases seen by the TSI) and have unfair terms and conditions – such as reserving the right to melt customers' gold down if they do not hear from them within seven days.

One victim featured on the BBC's Rip-Off Britain sent 17 items of gold jewellery weighing 132 grams to a website and was offered £150.29, or £1.42 a gram (the market rate is £28 a gram). When she declined, it took her more than two months to get her jewellery back. She subsequently sold it to a more reputable dealer for £7.65 a gram or £1,003 in total.

TSI's Sylvia Rook said: "There is a wide disparity in how much shops or dealers will pay for gold. Unfortunately there isn't much trading standards officers can do if people are getting a bad deal, provided the trader is not actually misleading the seller about the gold's worth. We can only urge people to shop around to make sure they are getting a fair price."

Laptops



As with mobile, DVDs and gold, a number of websites are vying for consumers' old laptops, including buymylaptop.co.uk, MirrorGoGreen.com and jaybrokers.com. But once again, sums paid are low and well below the going rate on eBay.

An old Apple Powerbook G4 with a 12" screen would fetch £60 with MirrorGoGreen and £100 with buymylaptop. At eBay, I found the same laptop selling for between £140 and £300. Whenever you sell a laptop, ensure its contents have been wiped so any sensitive data or financial details can't be exploited by fraudsters.