I know you won't but I'd recommend reading this write up from SBNation which will explain exactly why nothing is ever linked back to the school or the coach. You're never going to be able to get that "proof" that you're looking for, but that doesn't mean it isn't happening.
https://www.sbnation.com/college-football/2014/4/10/5594348/college-football-bag-man-interview
"Whatever the minimum of necessary paperwork to absolve a player of improper benefits received is, it's not a problem. A title for a moderately priced SUV can be created in a relative's name, as can a receipt of sale for a reasonable price.
"Hey, how'd he get that ride? His uncle bought it. How did his uncle buy it? Paid cash. Paid cash, how'd he do that? Shit, we don't know, but here's the receipt where he paid cash, and now y'all ain't got shit. Go tell the NCAA you think we're cheating because this kid's uncle bought him a used Tahoe in cash, you racist."
Remember, your job as a bag man isn't to hide the benefit. It's to hide the proof. In a region as passionate about college football as the American South, there's no real moral outrage when new cars or clothes or jobs for relatives appear.
"We can only get away with whatever's considered reasonable by the majority of the folks in our society. That's why it's different in the SEC. Maybe that's why we're able to be more active in what we do. Because no one ever looks at the car or the jewelry and says, 'How did you get that, poor football player?' They say, 'How did they get you that and not get caught, poor football player?'""