Certainly you need to worry about a customer who pays a debt with a credit card. But I don't think it is illegal.
Many years ago as a collector, if a customer came in and said this is all they had, do I want my payment(s), you betcha. I am on the receiving end.
Many small businesses have done this to survive. Some didn't survive, some did. Again, is it your desirable borrower, no. But should you refuse a payment because they are strapped, I wouldn't.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell