my biggest fear of buying used/vintage is the “why are they selling?” Every instrument regardless of make or price has the potential to be a dog. Bad neck, etc. Can i trust a seller to be honest, or even have the same expectations of quality as me?
You don't have to trust the seller in any which way. On Reverb, there's a 7-day period in which the item can be returned if "not as described". If there's a defect that I can't figure out within a week, I absolutely deserve to be stuck with that instrument.
People sell stuff for a variety of reasons, and I never inquire why. That's their own business. What I do inquire via the message system - if not stated in the listing - is whether the truss rod works, neck is straight etc.
I've bought quite a few things on Reverb and was quite lucky this far. I don't sell often, but have had only one less-than-desirable experience which was a combination of many things which very rarely line up altogether in a single transaction. The others were outright perfect.
My $0.02 only...