I've bought several computer related items on ebay, also sold a few with pretty good results. I generally stick to cheap parts when I look for stuff there though. I've got a KVM switch, keyboard & mouse, TV tuner, a video card and a few cheap used games. The only thing I haven't been happy with was the TV tuner, but I paid less than $20 for it so I can't complain much. I knew it was a high risk. I generally don't even look at complete systems or most of the components that go into a tower. I have been looking for a cheap video card for my kid's PC lately and have noticed a lot of stupid people paying well over $100 for used 256m 1950pro's. Make sure if you look at things like that on ebay you check Newegg also because they have some for $120 (or less if you count the rebate). Yeah, the kid's PC is still without a video card. I usually consider anything much over half retail price (current price, I don't care if you paid $300 for it 1.5 years ago) to be too much to pay for used computer components from ebay, not knowing the true history of the item. The seller could be telling you anything.
Ebay is a wonderful place to shop as long as you recognize it's limitations and use a little common sense. You also will need lots of time on your hands to find the best deals. If you're in a hurry to get something just go to Newegg, chances are you're not going to find many sweet deals in a few minutes of browsing. Also, not all sellers are quick to get the item shipped either. I've waited so long on an item before that by the time I got it I had already forgot it was coming.
Edit: Holy crap Dragon, I just seen the 1950 you have for sale. I, uh, hope you get what you want for it. From someone else.