I've bought a number of $100 and up items on ebay, usually without any problems. Where I got bit was in used computer components - everything from processors to hard drives to supposedly 'genuine' copies of Microsoft Office. I fell for the usual traps...if it sounds too good to be true, it probably is.
But I've successfully bought a used pedal steel guitar, amplifier, a Canon 30D with grip and goodies, a 200 f2.8L mark ii, and even my 80-200 f2.8L magic black pipe, and a new 580EX ii for an extraordinary price (I was nervous). I routinely buy genuine Epson ink on ebay, as it's 20-30% cheaper than going to Staples. In short, I think ebay has a wealth of bargains. As a sometimes seller (I've sold 2 lenses in the past 18 months, and other odds & ends), ebay and Paypal fees are brutal. So there BETTER be some protection for the buyer, and one of my bigger 'got ripped off' purchases, Paypal got my money back. So I have no complaints with their 'complaint department' at all.
But there are tons of scams on ebay. Whether you are buying 'mint condition' equipment or even 'new', there are as many crooks out there that either don't send the buyer anything, or what they do send is inferior, not properly described, or an imitation instead of the real deal that was paid for.
As mentioned above, it's necessary to do all the 'homework' you can on the seller. Check their feedback...at least 3-4 recent pages worth. As mentioned above, if they rarely, if ever, sell new photographic equipment and they are offering a new, in box higher-end camera, walk away. While I'd consider (and bought) a 'new, in box part of a kit' lens, I was confident that the description was accurate and it was a reputable individual (not store) seller. My 80-200 f2.8L came from a Japanese camera store with a rating in the 10s of thousands. The lens was perfectly described, the pictures were completely faithful, and I got the lens 2 days later! If there's -ANY- recent negative feedback for a seller, be doubly cautious. And if the negative feedback indicates bait-and-switch, rip-off, or condition issues not as described, buy from someone else!
As for the merchandise, for used lenses, my biggest criteria is condition as shown in the photos. Obviously, dust in the lens, if any, isn't going to show up in the photographs, so one has to trust the description. But I especially want to see the contacts, close up. The level of wear and tear on the contacts gives good proof of the lens being 'rarely used' or 'on and off the camera 100s of times'. I like 'mint' condition, personally. So I want very new-looking contacts. If the item is described as new in box and the contents are photographed, it better be complete. For a camera body, I'd look for instruction manual(s), CD, strap, battery, charger, registration, and verify all are present...unopened.
In the under $50 department, I don't have a problem dealing with overseas sellers...if they have a VERY good rating (8,000+). I had some computer parts take 4 weeks to arrive from China during the holidays. I was getting nervous, but they arrived undamaged. And if the deal is a rip off, $50 isn't going to hurt that bad.
