Given that the writer says he works up to 80 hours a week and "with diligence, someone working alone can make $1,000 per week" (i.e., ~$50k annually) I wouldn't

Given that the writer says he works up to 80 hours a week and "with diligence, someone working alone can make $1,000 per week" (i.e., ~$50k annually) I wouldn't call that a "quick buck". I've also donated a lot of used technical books to thrift stores and library sales, and if they're picked up and re-sold by guys like this that's fine by me.