I find that UPP has less stuff in stock because I think they take in less stuff used, but everything I’ve gotten there has been cheaper than the other two, arrives faster, quality exceeds expectations, and is packaged to survive anything in shipping.

MPB has more frequent different stock… middle on prices. Reasonable shipping times and packaging. Quality is about as expected and they do show the exact item you’re getting ostensibly… I’ve had a couple of times when something wasn’t right on the page but it was obvious like “that’s not a lens, that’s a tripod”. Generally they’re fine though. They do a lot of volume I think.

KEH has the most consistent stock. If you want a canon 50mm lens… they will have 3 versions of it ALL the time. Shipping about the same as MPB. Prices usually seem a little higher in general. I don’t like that they don’t show the exact item you’re getting though, which is annoying… but their rating system has been accurate from what I have bought from them.

Regardless of who you decide to go with, they should all have some kind of warranty for 6-12 months depending on what you get which is nice. Also, all of them will have a “join our newsletter and get a discount” thing. So maybe set that up a day or two before hand (sometimes it takes a while to get the email). But 5 or 10% off is still nice to have.