This has happened to me as well with FF shops, particularly from MF. It pissed me off so much that I completely stopped shopping for that client. Having spent money on 2 meals, neither of which I actually wanted, then being asked what kind of car I drove, what I was wearing, how long I stayed in the restaurant (info already in the report) in the hopes of identifying me and therefore, not paying me, was the straw that broke the camel's back.
After the third round of questions, I simply wrote back that I would not divulge the requested information and that knowing who I was was not going to make the counter any cleaner. I was paid and never heard back from them and never did another shop for that chain.
Managers with icky stores like to challenge reports because there's money involved in it for them. They get bonuses for perfect reports. When the reports are less than perfect, it is financially better for them to have the report rejected and therefore, maintain their "perfect" scores than to accept the report, work on the problem and lose the bonus.