Alot of the big names on ebay have their own site you can buy from, as well. x1387 is the same as plemix.com (sometimes sells under plemix, too), cti-miami (who I bought my N80 from) have their own website, hi-mobile.net, phonesourceusa, etc. If you pull up fonegrabber.com, you'll see the same sellers at the tops of the lists for whatever phones. x1387/plemix is usually the first one to post, though. everyone else quickly follows. I've bought several phones on ebay, no big deal. Just gotta know what to look for.
if it's ridiculously priced (If nokia said it was going to be $400 and you find one on ebay for $300 and there's only one or two on ebay at all, it's probably a scam.)
Good rule of thumb for ebay:
If it sounds too good to be true, it probably is.