I've just spent the day looking on eBay for a phone I really want.
I haven't bought anything yet (I have been eBaying for other low-value items for some time though without problems), but this particualr phone seems to sell on average for around £250-£300 (retail is around £350-£400) - anyway, I did notice quite a few ridiculously high offers like £1,000+ !! for the same phone. Most of these users had the sense to check out the bidders history & cancel the bids if at all suspicious.
It does make me think twice about selling high-value items on eBay (at least to international un-confirmed bidders)
The other downside is that PayPal is all to easy to allow you claim back money (that's how these scammers steal stuff) by claiming it was not received.
Best advice I can give is send only to a confirmed address if selling. If this is not possible, insure & track the item - this way you can proove to paypal that it was delivered.
If buying, make sure you read the sellers feedback ratings. If a user has been on eBay for example 4 to 5 years, but has a very low rating (i.e zero or one) I would be slightly wary.
Send them an email, if they are genuine they'll quite happily talk about the item.
I'm not sure if this helps you make your mind up, but in my own mind I'm reluctant to give anyone £200+ whether it's a high-street or otherwise
The thing is, unless your gonna get an absolute bargain, it is probably not worth the headache for the sake of saving say £30.