The growth of the Internet and low-cost airlines has turned last-minute flights into a big industry: just surf the web and there’s a flight cheap enough to buy on impulse and go on a trip this weekend. However, if you’re thinking about booking last-minute flights, there are a few things you should know.

One important point is that you can’t rely on the prices you see advertised for last-minute flights. This is because of the common practice of deducting booking fees, airport taxes and all sorts of little extras from the price, which are only added on once you’ve got your card out and are ready to pay, in the hope that you won’t want to come back then.

Also, keep in mind that a flight going to a big city like London or Paris doesn’t mean the airport is really close. Low-cost airlines use smaller airports to avoid the high airport fees of larger airports, and these smaller airports can be up to two hours from the city center with often unreliable public transportation. In some cases, you can end up paying as much as airfare just to get to the place you thought was your destination by train.

On airlines that accept seat reservations, it is also important to know that on last minute flights, the only seats available are the ones no one wanted, which are usually the ones in the middle of the row. This can be very important if you get motion sickness or if you really want to sit together as a couple or family.

The biggest catch is that last minute flights are always non-refundable. If you are going to buy a flight on the spur of the moment, make sure you can actually book it, because you can’t cancel the purchase afterwards.