Wealthy clients, like Trump, make it hard for the IRS as they can also employ fat cat tax lawyers to protect them.
But at that point, it's his legal team against their legal team, and the most likely outcome of that is a negotiated settlement rather than a court. There's nothing wrong with that - the Gov might get half plus penalties. That's particularly okay if the dispute is over a vague point of tax code, subject to multiple interpretations.
Oh yeah, totally not saying that it is BAD that wealthy clients have more resources to defend themselves, more so just bringing it up. It wasn't even a jab at Trump, moreso just saying that the IRS doesn't really have the funding to go against someone with the money to back themselves up.
If ya send a notice to someone who is poor and then force them to pay, they're going to do so.
If you try that same thing with someone who is wealthier, it's not going to fly.
People could debate if the IRS is always truly forthcoming about what you owe them, but that's for another time.
I really have no clue whether what you are saying might be true. The IRS doesn't really need "Lots of funding" to go against someone with the money to fight them. The case just gets settled informally, or like I mentioned, it goes to tax court and the judges decide.
If there's fraud on a billionaire's tax return, I would be very surprised to hear of cases where it was discovered and let go. The exception would be something like law enforcement wanted to let the guy run around for a couple years before roping him in, and so by agreement the return is processed normally. Maybe LEO wants to learn the entire network of drug dealers, then capture them all at once. Cases involving national security, you could expect that.