>>3510725If you're buying off of something like facebook, bring your camera and test it before you buy it. No one not trying to pull a scam will object.
Otherwise, just stick to the likes of ebay, adorama, or keh where there are protections in place if the thing isn't like how the seller describes it. The only thing you can possibly lose out on is time while dealing with it. Also, ebayers are so protective of their ratings they'll usually jump through hella hoops to keep from getting negative feedback.
You can get some protection doing the FB market thing if you use paypal to pay (MAKE SURE TO SCREENSHOT THE AD), but that's kind of hit or miss.
Places like fredmiranda are pretty reliable because the general public doesn't know about them.
Yeah, the cheaper Ls are usually the f/4 versions, the versions without IS, and/or older versions that are definitely inferior to the newer version.
But something like a 24-70 2.8 II IS? You can expect a good condition one of those to go for around $750 all day long for a long time.
