Confused

[j4]

Trying to set up an eBay seller's account and I'm confused already. It wants me to fill in a direct debit mandate -- are there regular fees for having a seller's account even if you don't sell anything? I couldn't see anything about that but I can't see how you can set up a dd to say "please debit however much these people need from my account whenever I sell something", you'd basically be signing a blank cheque.

And they've already asked me to keep card details "on file" to check I'm me, and to nominate a card to pay from, as well as an alternative card to pay from, and I'm running out of cards!

Having seen some of the people who apparently manage to sell stuff on eBay with no difficulty, if I can't do it I must be so stupid that it's amazing I managed to work out how to breathe. :-(

Update: Huh? "You are already a registered seller!" How'd that happen then? I've never tried to register as a seller before...