money talks, I've always sold stuff on the basis of whoever gives me the money first will get the item. I've had guys sit on a decision for days and had to turn guys away who actually had money in hand and then they go off and buy from someone else. I will hold items a maximum of 1 day as a result. Either have the money ready or be prepared to lose the item.
conversely I've had people local to me promise to buy items and then never be concrete on a pickup day and eventually never return a message. All the more reason to ship it to the first guy that has money in hand.
Oddly enough this has only ever happened to me with airsofters. Everything else I sell used I always get buyers with cash in hand and they show up and leave with it that day.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.