All payments I take are always via PayPal, so at least both parties have some protection.
Bank transfers are only taken from established companies, not from private individuals.
I've sold on Gumtree a few times, but will only ever deal in person, so the customer can check the item, and I then check the cash!
I no longer accept cheque or postal orders. I've been done by fake postal orders once several years ago, luckily it wasn't a major amount.