I’ve had one client charge back. It was exactly 3 months after the inspection to the day and they claimed it was an unauthorized charge (they did not buy the home) It took about 2 months for PayPal and the Credit card company to research it. They ruled in my favor and returned the fee. However, for this PayPal charged me $20.
Make sure you swipe and they sign your phone. It is much harder to claim fraud with a signature and card was present for the transaction.