Class Cheaters

I attend UCI and work part time at a retail store near UCI. I have a regular customer who I chat with quite often, he introduced himself as a sub teacher. After a few visits I find out he takes tests for college students online for a significant amount of money as a side hustle. Hey was recently telling me how he took an Ochem and Bio-chem test for UCI students. I wouldn’t be so concerned except for the fact he is always discussing how these are students who are pre-med or in the medical field. Is this a common thing for students to do?