They're probably not reporting it or/plus they're probably paying illegal workers with it. No other reasons to give 10%. If I was an IRS agent and I saw that, red flags would wave immediately. Anything beyond a 3% discount because of credit card fees is suspicious imo.
This is just one guy's opinion. I may or may not own any of the tickers I am posting about. I am not compensated nor do I have any desire to be. Do not buy or sell based on this post.