Some people will let you finance them if you allow it, and from what I've seen, once a slow pay, always a slow pay.
This is so true. I used to be fairly naive about this, but I learned my lesson from experience. Some of these taxpayers are professional grifters. And if they aren't paying the IRS, they aren't going to pay you, either.
I remember one guy in particular was crying poor to us, about how he couldn't afford to pay the bill, but I used to work at an optometrist's office when I was in HIgh School and the guy came in wearing a new pair of designer glasses--I know the brands because the high-end ones usually have a distinctive logo on the temple. Just the frames were upwards of $600, and I could tell that the lenses were premium ones, too (anti-reflective coat, etc). The glasses put him back a pretty penny. If he was "poor" he would be wearing something more affordable. I didn't mention that to him, but I refused to let him have the return without paying. He mumbled and grumbled but he handed over the payment.
A lot of people are scammers. Just because YOU aren't like that doesn't mean that other people aren't. It's kind of depressing when you start to see the world for what it is.