Refunds and withdrawal
A listing goes up the moment your payment clears, which is what you are asking for and also what ends your right to change your mind.
Withdrawal
Your listing is published immediately, so at checkout you are asked to expressly consent to immediate performance and to acknowledge that this ends your 14 day right of withdrawal under EU distance selling rules. Listings are non-refundable once published, including when somebody later contributes more.
The consent is not buried: it is a box you tick at checkout, and the payment button does not work until you have.
Being passed on the board
Somebody contributing more than you later is not a fault and is not grounds for a refund. It is the thing the board does.
Your listing, your name and your link stay where they are, with the amount you contributed. Nothing you paid for is taken away.
If a listing is removed
Listings and links may be edited or removed at any time without notice, including on request of a rights holder, and the service may be discontinued at any time. Amounts already paid are not refunded on removal for breach of the link policy.
If something went wrong
If you were charged and no listing appeared, if you were charged twice, or if the amount is not what you agreed to pay, write to [email] with the date and the amount and we will put it right.
This is separate from changing your mind. A payment that did not do what it was supposed to do gets refunded.