I agree with the points raised so far.....You're running a business.
But just thought I'd point out a flip-side.. ...to the arguement.
Your records are always priced well, so it's near on impossible, as you well know, to get to you quick enough to snap up that well wanted single.
The first time I managed to be the first to get one....I replied straight back with my card details and waited for the postman.
After a few days, being the impatient person I am.. , I e-mailed you back asking where it was...
My e-mail bounced back.....
I posted up on ss to find you, thought the aliens had wisked you away....
Turns out you hadn't receive my e-mail with the details and had sold said record....
I didn't throw my toys outa the pram, as I realised sh.. happens...
I will fone next time.....
So, a thought might be....if someone is the first to ask for a record, they should then fone you with payment straight away or risk losing it.
PS.....I did tongue in cheek, ask how you wanted payment at the beginning of the e-mail....serves me right....