I had a recent bad experience with
RobertsCamera.
They had a DA-L 55-300 for Buy It Now of $45 (+$12 shipping) or best offer. Descriptions said 'Not Tested, sold as is" but there were multiple pictures (7-9 ish) showing the body looked great and the glass was clean and clear. I figured just might not want to mount to a camera and test since it is a cheaper consumer zoom with a lower profit margin. I offered $29 figuring it was a slim chance but they accepted (at which point I'm obligated to complete the purchase per eBay TOC). When it arrived I found the zoom ring was VERY stiff, to the point I would be afraid of breaking it further if I forced it any more, and the focus ring wouldn't turn at all. For the amount of handling it took to get the pictures in the listing, there's no way any competent camera company employee wouldn't notice that the lens was obviously broken, even without 'testing' it. I looked at some of their other listings, and they show other zooms extended and un-extended, so I'm sure they noticed that this one wouldn't extend. Even a camera lens novice could figure out something was wrong. Basically, they took an
obviously broken zoom, labeled it as 'not tested' and sold it to eager me. I'm not the only one to fall for this either if you look at their
feedback.
Luckily, I was suspicious before I even made an offer, so I had an idea of what I might be buying beforehand. I have another 55-300 with a chip in the front objective and some slight haze, so I had a backup plan of merging the two lenses to make a fully functioning one if I couldn't get this one to work. I have since taken the broken one apart and found that the front was shoved back, cracking some internal plastic stops and jamming the focusing helicoid. I got it to go back together correctly and it works, but if you focus past infinity while at 300mm it slides out past the cracked stop and jams again, so I'll instead be moving this clean glass into my other lens. (Still on my to do list.)
Like other have said though, I will only buy items with actual pictures (camera gear or used phones), and I make sure to ask specific questions about expensive items so I have things stated in writing in a message that eBay administrators can see in a dispute. Important questions are fungus, haze, is the aperture slow, and most importantly "Is the item fully functional". If they respond yes and it isn't, it's an easy dispute if they don't agree to a refund.
Another note - Feedback is permanent. Use the item for a week before you leave positive feedback, and try to work it out with the seller before you leave negative feedback. It's hard to make a case the item is broken if you leave a glowing review a day after you receive it and find the issue a week later. I've also had times where I ended up leaving positive feedback after receiving defective items since the seller worked so hard to make things right.
---------- Post added 09-25-17 at 01:42 PM ----------
Just to add, ever since I upgraded from a point and shoot Canon, all of my bodies and lenses have been bought used. Most of my expensive gear (flashes, strobes, carrying bags) has been used as well. The only things I've bought new are lens filters, a tripod, aftermarket batteries, and SD cards. (Though I have a used 128GB microSD in my phone.) I have had many trouble-free experiences buying used equipment, and also some great experiences when I actually communicated back and forth with the seller a few times. My most recent purchase was from
HuntsPhotoandVideo and they were good about answering my multiple messages and questions before I clicked Buy-It-Now.
You can get some really good deals on eBay or PentaxForums. The key is to be careful about looking at descriptions, ask pertinent questions, and be patient. Eventually you'll catch something selling for less than the average selling price. (The best deals are at odd times when people are asleep or at work, or someone just posted a Buy-It-Now at a low price just to get rid of it.)