How did you know that these machines were paying over 100% return? As far as I know the only way to get over 100% on BJ is by card counting (even with surrender)which doesn't work on slot machines since they reshuffle after each hand. If they were paying at less than 100% then why not just go to a table and give them your card to get rated?

I guess if you played perfectly and the machine was set to deal only single deck BJ you could get a little over 100% (with the slot card cash back)but I am not sure how much you lose by not being able to double down on hands other than 10 and 11. It may be more than the .7% profit you get from the slot card. Does anyone have the exact numbers?