You'd be surprised. Small business owners are notorious for running non-deductible personal expenses through their business for example when they really shouldn't. Plus some super egregious stuff I can't begin to get into here. It is trivially easy and the state/fed gov can't begin to crack down for lack of resources. These are your tradesmen like plumbers and electricians, boutique shop owners, salons, food/catering, smaller self employed professionals like doctors, lawyers, therapists, dentists, etc. It's sort of a grey area and there's wiggle room for sure, and I try not to let my clients get away with all of it. But I do look the other way a lot and just plug my nose and sign it and push it through when I'm in a hurry, which is basically always. Some people are just maniacs though, it's really staggering, idk how they sleep at night. Smaller numbers than a hedge fund manager making $50 mil, but it adds up real quick, and fraud is fraud IMO.