More, in terms of charge backs. Less in terms of fraud.

No, you can charge back onto debit cards, longer than credit cards.

Different fees on their end for one.

Also, their are different time scales for people to charge back on credit cards vs debit cards.

You can technically register it and send him a letter saying to stop using the name. He would need to prove in court he was using it before you, which jt sounds like he can. You would most likely lose. He might change it rather than fight it in court.

Not worth it either way. A name alone doesn’t make a company.

Reimburse milage or depending on the situation, give them a stipend.