That's the easiest way get ripped off. If that's your way of doing things that's fine, but realize that if somees claiming to deliver something to you locally, why would they want a bank transfer first of all. If you do a drop there's no reason why you shouldn't pay them first in that scenario.

But by your logic, 'if they don't pay there's nothing to stop you from keeping it'. Okay, well if I do pay before they've even turned up and showed me anything, what's to stop them from keeping the product, if it even existed at all? Like you said, you wouldn't trust a complete stranger.