Actually I don't. I *always* charge 300 bits, but use bitcoin core to estimate how much fees to apply, so that it confirms as fast as possible. Sometimes it requires that I pay less than 300 bits, and sometimes it requires I pay more than 300 bits -- but that's irrelevant for the person making the withdrawal.

The issue here seems to be not that MoneyPot has dynamic fees (That's the correct thing to do) but rather that they're paying too low fees, and people aren't getting their withdraw in a timely fashion. I guess my question to them would be "What are you targetting?"

In bustabit, I'm using bitcoin cores 0.12.1 estimation (which is a 95% chance of confirming within 2 blocks) although in practice >99% of all withdrawals confirm in the next block that has transactions.