Not sure if this is helpful to you or not, but I actually learned a lot about used equipment by searching ebay. Most camera sellers are pretty honest about any flaws in their equipment, so through their close-up shots I learned about spotting fungus and mold inside a lens, checking the mirror for any damage, and that shutter count is important. The things I learned from searching through those listings provided the direction needed for further research and eventually I was spotting things not mentioned by less scrupulous sellers. If you’re just starting out, browsing through hundreds of sales can teach you a bit.
Sorry I can’t help with the particular cameras you are asking about (I actually shoot with Canon equipment), but I’m sure someone else will be along that can help with that.