Rich people may think twice about injecting "shady" blood into their veins though. I mean, many seem fine to do it with intravenous drugs but at least you won't find AIDS-laced heroin.

I think it might make more sense for super rich people to pay people directly to give them their blood, which is morally questionable but maybe not particularly worse than, say, paying for a surrogate mother? It sounds a lot less traumatizing at least, both physically and psychologically. After all many people do donate their blood for free several times a year.

I'm pretty sure you could convince many young people to give up some of their blood for a pretty cheap price actually. No need to resort to kidnapping and slave farms.