In case anyone else has the same problem I did, here's how to pass the "Shop" class. Even some of the posts by console users trying to help don't explain this properly.
From what I've read, console users have to turn a thumb stick to rotate the bike's pedals when instructed; on the PC port you have to rotate the mouse in the direction indicated, in the same way as for picking the combination locks on lockers.
In the shop class, I couldn't understand why on each try I got failed the moment I moved the mouse. It turns out the trick is to be already moving the mouse
before the instruction is displayed. This usually means failing a few times to learn the sequence, but you'll get there in the end.