Why is it so hard to buy parts from people

makes sense on the swap meet but there are so few of them it seems. i went to clay city ky for the latest swap and it was not too good on friday but real good to me on sat. but there are things that you don't think to take that someone asks about. i try to list things that i don't really need anymore. things that someone else may need. i try to ship cheapest way possible and hope it is cool with the buyer. i am usually open to negotiation on price but not all the time. i had a guy ask for phone number to send pics of parts. got pics and now crickets. just never know about people.