For background, I'm from the UK, where people donate blood, plasma and platelets, and AFAIK, it's illegal to sell such things. I read all kinds of things about US health care on HN, but this isn't something I've come across before. If true... I don't know exactly, it just feels very, very strange, especially for a "western" country.
For example, there is a scene in https://en.wikipedia.org/wiki/The_Pursuit_of_Happyness where the main character sells blood for money.
You can find several websites that mention this "money making strategy": https://www.thepennyhoarder.com/make-money/240-month-selling...
Selling plasma for cash is mostly done by very impoverished people. I used to live a few blocks from one of these businesses. The people you see hanging around the place would probably discourage anyone but the neediest from "donating."
Yes. An acquaintance who has a Masters in CS (but no experience so they're finding the job search tough) sells weekly.