I've done this many times and never had a problem. It's probably going to happen a lot more often now since eBay put their charges up (10%, max £75 up from £40).
The golden rule here is to buy the seller. Check his feedback, get extra pictures etc. most people are honest and will happily do almost anything you ask in order to prove they're genuine. If he's not prepared to do something reasonable then it's best to walk away.
Dave