I have bought quite a few things on eBay and have really only had one or two main problems. All the tools I have bought turned out to be ok, including a new 18 volt Dewalt Drill with two batteries for $150. The only problems I have ran into involves computer parts that I bought for my personal use that turned out to be fried.
The main thing is to watch yourself. Check out the sellers rating and read comments about them. Don't buy second chance auctions because most of them are fake or scams. Only sign in from going to ebay.com and using their main page. Most other sign in pages once you are already in are fake. Use paypal so you can file a claim if you need to get your money back. Also beware of carefully worded scams that seem ok at first. Many people were selling X-box 360 boxes, which seems fine at first glance when they have pictures of the box and describe it, but after paying attention you actually find out that you paid $600 for a box.