I've used Gumtree for buying and selling, it's great, but for me it has always been person to person. Yes, actual human contact, I know
Its great because there are no fees and you get cash in hand when selling. I guess if you find something you really want that is too far to do a meet up you could ask about posting and online payment etc. But the safety nets aren't in place like e-bay if you pay someone and they don't send you the item.