As someone that provided development and system administration support for multiple payday lenders for a few years, I will say that their adherence to the rules each state enforces for payday lending companies I dealt with was often "spotty". It was a regular occurrence that they would have a state regulator visit to look at their operation, and they would all of a sudden be scrambling to make one or two accounts that they had completely dropped the ball on disappear. E.g. where they had rolled over a bi-weekly payment of $125 on a $500 loan for over 50 consecutive weeks.
Let's keep in mind this is the industry that responded to legislation that you can't have the loans continue past a few periods by laving that last payment immediately preceded by another loan of the same amount, of which the amount needed to pay off the prior loan was immediately subtracted, resulting in zero difference in payments, but a new loan on the books. IIRC, for some states that required the loans be paid in full at the first opportunity, it meant a new loan was issued every pay period (that is, loan of $500, two weeks later a new loan of $500, which is used along with a $125 charge to close out the prior loan balance of $625 and issue a new $500 loan, continue as long they're unable to pay off the loan amount of $625).
There is some benefit to the system though. I did see plenty of accounts where the customer paid it off in full at the first payday, which still results in a large fee, but that's acceptable for people getting same day short term loans. There's also quite a bit of defaulting on the loans, which means there's some justification for the high fees/APR. It's just where the system is abused and customers are funneled into systems used to milk them for large amounts long term where I was particularly upset by how it worked.