I work for a bank so hopefully know what i'm on about.
As a seller- If they pay cash in a branch you are sorted, nothing to worry about even giving out your details it's the same as what's on a chq, only thing is if they send as a standing order as they can be recalled on the same day.
As a buyer- This is where you need to be careful, a lot of e-bay scams are done this way, cash paid in goods never sent hard as F**k to get your money back as the bank can't do a lot to help you, Always pay-in at the counter and get a receipt.
Anything else give me a shout.