if someone calls you or gives a real phone number to you, and is then willing to give you cash, you can make arrangements to see it or have it seen. try to sell locally or within driving distance. shipping can be a problem if breakage occurs.
they should come with cash in hand and take it away. if it's a small something, meet them some other place, like a library. in a case like that, they don't even have to know where you live. if it's large or has to be plugged in, they must call for the address (get a feel for what they sound like) and make an appointment to see it. they have to bring cash and take it away. tell them before they come, they cannot come inside the house. borrow a large, loud dog. seriously. show the item in your driveway. they shouldn't know what else you have.
if someone is serious, it's a simple deal. once they start telling you a story about why they can't do this or have to do that, forget it.