Look in physics, for example, nobody is going to take exams for you, you have to know the subject, there are no papers to write etc. Most engineering courses are that way except for labs. The only way to cheat in these type classes is to bring a cheat sheet with formula etc. on it. Some profs let you do that so there is no way to slough through.
Back in the early 70s there were students who hired stand-ins in my organic chemistry classes. The class was large enough that the professor never knew everyone. The ‘goats’ also did the labs and took the exams. They were usually grad students from another school who had already taken the courses and/or had an expertise in the area. Not done much in seminar courses but a lot in the lower to mid-level courses. The “employer” wanted the A grades for other purposes such as to get into med school where they didn’t have to take organic or physical chem or even a grad course in microbiology. They just had to have the general background, not the detailed knowledge to make it through the actual medical courses. I knew a couple who made it in that way. Gave you the urge to go to faith healers rather than some who ended up with their MD degree.