I buy only used camera bodies and lenses, mostly from Amazon here in Japan, due to their straightforward returns process. I have bought one of my E-M1 IIs from a retail shop specializing in used camera gear, called Fujiya. Camera gear is handled differently in Japan than in the US: generally it is in better condition than US eBay stuff (my only other online experience) with items listed as “Very Good” looking like they are brand new, just missing the original box. “Good” items arrive in “Very Good” shape, and so on. Japanese consumers seem to take good care of their stuff. The only unusual risk here is fungus, which I never encountered in the US (west coast). But, as with all other possible issues, Japanese sellers are typically quite honest about that, and post several clear photos of each product, to reduce ambiguity. Japan listings do not include shutter activation counts, though.
Prices are lower here than in the US, which I think is due to a more active photography scene here. I got both my E-M1 IIs for under US$515 apiece, for example. The first one had a good patina (clearly described and depicted in the listing) and ~30,000 shutter pulls. The second one looked new and had fewer than 4,700 shutter pulls. I was pretty happy about that.