You are wrong. Gambling sites WARN not to use Coinbase or Xapo because when Coinbase detects that the "deposit to" or "withdraw from" comes from/to a gambling site they might ban the account holder. Usually they just give you a warning a first however.
However even if they BAN the account holder, they always let the deposits come through and then they make your withdraw the fiat funds.
We WARN too need read rules.
but we can't ban acc
Yes but its not your problem if the account holders Coinbase account gets flagged or shut down. You should at least still send the transaction to that address and if they have an issue with it, then its fair fault.
Like the previous user said before, you are just using this as an excuse not to pay up. Because if he sent the money FROM coinbase to you, then most likely coinbase already knows he is a gambler and it doesn't make a different if you send him back his funds from your website to his coinbase account.