You can do a lot of reading about this online, if you want to.
The issue with the fraud checking process for PIP is that they pick a sample- in 2024 this sample accounted for 0.06% of claims- and they contact the claimants and verify info. How many claimants do you think answer that call and say “ha, joking, fooled you didn’t I”? Zero. The only way to accurately check for fraud with PIP would be to have feet on the ground people actively investigating and look at what people are doing, not just at the info they provide when asked. We don’t do that because there isn’t enough money to have people out doing that, but there would be plenty of people who fill the forms in to say they can’t leave the house alone, can’t go to the shop, can’t go to the toilet unaided and actually if anybody was bothering to perform in person checks on any given day would see those same people walking down to their local shop, sitting having some lunch in the cafe etc. I know a few of those just personally myself, one woman who did get reported as someone had literally compiled evidence of her doing everything she claimed she couldn’t do.
UC fraud is easier- but still not easy- to cross check, who’s earning what money, HMRC have the payslip info, who lives with you, savings limits etc. PIP fraud checks would essentially rely on someone deciding to change their story, unless you had people actively out looking.