I strictly stick to eBay or Amazon for a simple reason, they both protect me as purchaser if something goes wrong; with eBay you have 30 days protection (I sent back, in 20 years i buy there, 4 or 5 items, and I always got my money back), with Amazon even better because with "Warehouse" you're buying not from a private person, but from Amazon itself, so if the return is not good (of course it happened to me, more than once), you just sent it back and you got your money back in like 24/48hrs.
I prefer a deal on those platforms to a deal in person, even from a friend, because if the item fails, I guarantee you it's much harder to get money back from a private, especially if it's a "friend" (a REAL friend of course poses no problems).
Examples on eBay?
The EF 24-70 f2.8 L Mark II, just fully serviced from Canon (aperture iris was changed, which is the only real issue with that kind of lens), paid this summer 610€ shipped (663$) just because the outer barrel had a couple of REALLY light chips, and plastic hood lock was broken (I bought a third party hood for 10€). I think that actually was my luckiest deal in 20 years on eBay, I admit.
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Or just before Christmas, a basically brand new (was a shop demo unit) R10 kit with 15-45 and the RF to EF converter, bought for 735€ shipped (800$); when I re-sold the kit lens (150€) and the EF-RF adapter (100€) I had a final price for the body only R10 of 485€ (530$), like a Eos Rebel, but for a much newer camera, and believe me I can resell it tomorrow body only for the same price I paid it with all the kit stuff.
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Amazon not really big deals on cameras and lenses because even used they have stellar prices (for those eBay is way less expensive as you just saw), but i got a lot of studio stuff (light stands, COB leds, reflective panels and flags, boom arms, softboxes and modifiers in general, clamps, etc) from Warehouse for half price or less, and lot of the stuff is prime brands (Manfrotto for instance), not just Chinese stuff.
(I have to say, I have a special fiscal treatment were I pay really low taxes, but in exchange I cannot expose my professional purchases as costs, so I have no reason to buy new with the invoice, because I can't deduct the gear from taxes; so that's why always prefer to go used. Anyway, I often buy stuff, if the deal is good, just to try it, and lot of the times I end up reselling it for higher prices, so my "eBay & Amazon game" is also a sort of side business, that gets me extra money on top of the rest).