I think your friend is full of bologna. Is it possible that there are stolen parts on Ebay? Yeah, I am sure there are a few, but probably a VERY small percentage. I certainly wouldn't avoid buying parts on ebay because of the possiblity they might be stolen.

You can usually save a little on parts on Ebay compared to LBS, depending on what you are buying. Typically the higher priced the item, the more you will save. But you often can find parts for just as cheap buy going to Performance Bike, Nashbar etc.

The thing with bikes as a whole on ebay is that it really is a seller's market. You can find decent deals, but steals are virtually non existant. There is simply too much traffic on ebay to find GREAT deals. If the deal is great, the odds are somebody else will either snatch it up if it is Buy it Now, or drive the price up if it is an auction.