Just to add in case anyone is in any doubt, there is no such thing as abusive play with bonuses (if the terms don’t clearly disallow something). The only real difference between players is that some are there for the bonus only. They can and will often play just the same as other players (i.e. those after the bonus don’t always know how to play). Conversely, even many loyal players will make the most of a bonus and many will play to maximize the return the same way as expert players so the whole idea is flawed and also fraudulant as you are offering the bonus and giving it to players who you will later deny.
Another thing, is that normally the expert players will play large bets with the bonus and look just like a high roller. The other players just looking for the bonus will be almost the same as your average player in terms of the cost to you (assuming the promotion has a cost to the casino in the short term) so the only problem is if there are a large number of them. There is no way you can tell which is which. If you want to stop players taking any more sign up bonuses judging from their lack of non-bonus play, then you have to do just that (not give it to them) and not decide after they are given the bonus which is potentially fraudulant if the reasons are not verifiable and fair.
Casinos always knew a certain percentage will only play for the bonus and this should be factored into the cost. They really are stupid to ‘get back’ at these players with ridiculous behaviour like this. In the past this only happened at the dodgy casinos trying to get back at bonus players (like you are doing) or those about to go out of business and in desperation. Even when Gaming Club tried something five years ago, they saw the error of their ways and apologised.