Emma
I don't know if you might know this already but there are many scams related to mobile phone buying/selling on Ebay.
If you go to Ebay forums and look for advice on how to sell a mobile phone, it'll give you all the details, but here's some basic advice in case you've not heard of these things...
Don't put the phone as a "Buy it now" but only as Auction. This is because if there's a buy-now option, the scammers jump in and buy it straight away. With Auction, they don't have so much patience (apparently) and also you can monitor the auction and cancel any unsuitable bids just before closing.
Block any buyers with negative rating score or, in my personal opinion, for this particular transaction I'd say block anyone with rating of less than +50.
DO NOT SELL YOUR PHONE to anyone from Nigeria, other parts of Africa or Eastern Europe. I know this sounds like terrible, terrible discrimination and I offer huge apologies to anyone from those countries who might be offended by this (I'm Serbian myself so I know how you must feel). It's just that these are the places where the scams seem to originate from.
The scam looks something like this. You put the phone up for sale, (especially if buy-now), then you get an email from a person telling you that their boyfriend/sister/dad lives in Nigeria or any of those other places, and asking you to post the phone there urgently because it's a delayed birthday present or whatever. They usually say they're happy to pay over the odds for postage (or even the phone itself), and either say they will transfer money to you straight away or that they've already done so. You may even have an email from PayPal or similar company saying the money's been transferred (and often showing a much bigger amount than what the price actually was). THESE ARE FAKE EMAILS please do not trust them. If you send the phone, you will never ever see your money.
It's one of the most common scams on Ebay and personally I'd say sell only to UK and to a reputable buyer with high score and good comments. If unsure, ask for their tel number so you could have a chat. A genuine buyer won't mind.
My boyfriend and I have read about this and didn't really know whether to believe it, put a phone up for sale with a buy-now option, within couple of hours we had 5 emails from different people from Nigeria all claiming that they've bought it and with all various emails confirming payment !!!! Those emails from Paypal look completely genuine but don't be fooled, they're fake, and on checking sure enough there was no payment in his account.
He had to re-list the phone 4 times before managing to get a genuine buyer.
Hope this helps mate.......