because they double checked and the customer got huffy about it

customer did this to themselves, OP tried to help them and was punished for it

I wasnt a professional, Just the "computer guy".. and its been like 25+ years, but if I recall correctly they didnt hire me to reformat it specifically, I believe it was windows 98, and memory serves it hadnt been reformatted in years, and i think they slapped some new PCI cards into it without removing the software for the old ones? I dont remember the details, but basically told them that a clean start would have a 98% chance of fixing their system, and if it didnt.. I'd still need the clean start to figure out what was wrong where.

They were over my shoulder the entire time, wouldnt have let me if i wanted to (Edit, and I wouldnt have wanted to, because I hate going through peoples stuff even with permission).. and quite frankly I just wanted to get out of there asap cause I didnt like the attitude i got for being there trying to help them.

I did run into them again at a later time, where they were sad to have lost their stuff, but said the computer was running faster than ever, not realizing how much the bullshit had been dragging them down.

"Why didn't you go against the customer's wishes and dig through their data after being told to proceed with the task you were told to do? You could have extorted them while showing you were willing to violate their privacy and steal a customer's data!"

FTFY

You could do it in a less criminal way…

Back up the files, then, when they discover the fuck up: "I can try to recover the files, but it's going to be a lengthy process. I'll have to charge you $x."