You've paid for your seat, turned up on time and next minute you're being asked to leave the plane.

That's what happened to a passenger on United Airlines because the plane was overbooked — but he was dragged off the flight when he refused to move.

Overbooking happens in Australia too, in fact an expert says it's fairly common. And while airlines here differ on what happens next, you might be able to turn the situation to your advantage.

Here's what you need to know about why airlines do it, and what you can do if it happens to you.

There's a reason airlines overbook flights

Overbooking in Australia Check in early to help avoid any issues. Once you have a seat assigned you're less likely to be bumped

Check in early to help avoid any issues. Once you have a seat assigned you're less likely to be bumped If you are bumped, ask for an upgrade, sometimes airlines will offer incentives to get you to switch flights

If you are bumped, ask for an upgrade, sometimes airlines will offer incentives to get you to switch flights If you can't get on another flight, ask the airline to cover any on-costs such as accommodation

Airlines often sell more tickets than there are seats on the plane.

They're betting on the fact there's going to be a certain percentage of people who don't show up.

It's a fairly routine practice and it's sold as a way for airlines to keep prices low.

If everybody shows up, they'll often ask for volunteers to give up their seats for some kind of compensation.

And airlines are totally allowed to sell more tickets than there are seats

Thomas Janson is the department manager of transport law at Shine Lawyers.

"Overbooking is legal in Australia and unfortunately it is a fairly common occurrence," he said.

Research by CHOICE found 21 per cent of Australians experienced flight delays or cancellations in 2015, and 4 per cent of those were bumped from their flight because of overbooking.

"Under the Australian consumer law airlines are required to provide services with due care and skill," CHOICE spokesman Tom Godfrey said.

"If the airline makes a mistake and overbooks your flight, it is required to rebook you on the next available flight or give you a refund."

So I've been bumped. What happens?

There's no uniform rule on what happens next in Australia, according to Mr Janson.

Sorry, this video has expired Video of a United Airlines passenger being dragged from an overbooked flight has sparked outrage online

"Unfortunately, the rights of Australian passengers are fairly limited in the context of domestic flights when they are at the mercy of the conditions of carriage of the particular airline," he said.

Here's how some of the overbooking policies of major airlines in Australia compare:

Qantas: An "incentive for volunteers not to travel on their booked flight" will be offered. Qantas policy also states it may " deny boarding to one or more passengers involuntarily " if there aren't enough volunteers

An "incentive for volunteers not to travel on their booked flight" will be offered. Qantas policy also states it may " " if there aren't enough volunteers Virgin: Passengers can be moved to the next service at no cost, and be "entitled to refreshment vouchers at two-hour intervals while you are in the airport awaiting your service". If that flight is the next day, they'll pay for hotel accommodation, transport to the hotel and $50 per person for meals

Passengers can be moved to the next service at no cost, and be "entitled to refreshment vouchers at two-hour intervals while you are in the airport awaiting your service". If that flight is the next day, they'll pay for hotel accommodation, transport to the hotel and $50 per person for meals Jetstar: You'll be moved to a flight to arrive "within a reasonable time of your original scheduled arrival time". Jetstar doesn't list specific compensation in their policy, only that you may be entitled to some form of it.

Australia compares pretty poorly to the rest of the world

Mr Janson said Australian airlines weren't great at looking after passenger rights when it came to overbooking.

"There seems to be very little appetite by government and the ACCC (Australian Competition and Consumer Commission) to look into this issue," he said.

He cites the European Union as the gold standard when it comes to looking after passengers on overbooked flights — and CHOICE agrees.

There, you're entitled to be given up to $900 if you arrive at your destination more than three hours after you were supposed to (with extraordinary circumstances like weather excluded).

You can then get meals, two free phone calls or emails, and hotel accommodation if needed.

"Unlike Europe, Australians are not entitled to set levels of compensation if their flight is overbooked and they are delayed," Mr Godfrey said.

"Whether you get a meal voucher or just a pat the back after your flight is overbooked, is at the discretion of the airline. There is no requirement for them to compensate you for your loss.