If a program is going to shave you, its not always going to be a straight % off the top ... which is easy to test for, you just do a test sale every now and again (& inform the program owner once its showed up in your stats so they don't think you are cheating).

Some programs have been caught out doing things like redirecting joins to a different processor etc, so having access to the processor stats is not going to help you if the joins aren't making it to that processor.

As Dawgy said, it comes down to how much you make per click at the end of the day.

Is that what you meant by 'fixed'?