The current transactions fee of 3000 satoshi is hardcoded, if in any case the transaction fee is higher than 3k we're paying the missing amount from our bank.
In any case you own 13k and withdraw 10k you should end up with 0.
Hardcoded means that 3000 satoshis is a fixed transaction fees, no matter what amount of withdrawals. If in cases, users require withdrawals that have more than 3000 satoshis in fees on network, the site will pay for the rest fees as kind of supports for users on the platform. Do I understand your clarification correctly?