As above it a very well known scam which people often get away with, “I’m going to pay over the phone and my “mate” will pick it up later” then the payment is returned as it was a stolen card.
So don’t bother with that rubish, Often a deposit is required if they are buying £x ammount of stock they wouldn’t normally have but most shops would let you transfer the deposit if it was the wrong size etc.
When you say try do you mean sit on or have a proper test ride?