A few months ago I sold off some gear after downsizing some hobbies. A few things I learned:
First, after a number of strange interactions (requests to drive halfway across the state, unreasonable holds, people flaking, etc.) I camp up with the following boilerplate for every post: "First come, first serve. No holds. Cash only. Must pick up in [my town]." This mostly eliminated the crazies, though some people still ask!
Second, I learned to accurately document everything about the item in the post: condition, make, model, year, dimensions, damage, etc. If when meeting with the buyer they decide to start negotiation down or try to lowball, unless there's some condition I didn't know about (e.g. damage I didn't see), then I just start packing things up and drive away. They knew the condition and details before meeting, not interested in their BS. The fact that they drove to my town (usually a public parking lot) means I don't feel pressure to accept a lowball offer or to haggle over price.