Unpopular opinion, but I'm OK with eliminating this loophole.
I went to a record shop a couple of weeks ago and when I went to pay, the guy didn't take Apple Pay. Or any kind of credit card. All he took was Venmo and Facebook. Fortunately, I had cash. But if you can't even shell out $5 for a Square reader to take credit cards, you're not a business — you're a hobby.
And yes, I have owned small businesses before. Three times. Each time, I took credit cards as payment. It's known as "cost of doing business." No different than paying to put up a sign, or renting a storefront.
If you're doing a relatively low volume you might get away with it, but you are committing a crime.
However, it is definitely against the terms of use and will get their accounts suspended. As PayPal has shown, they might also confiscate any money left in the accounts.