You need to prove that this customer is willing to spend, and that you have provided suitable products and services.

Documents are evidence, and other things can also be evidence, such as videos.

Really not, such as the cashier's statement, you can also prove that it is him.

In this case, you can try to contact him with a lawyer and tell him that you have evidence. If he lies in court, he may commit a criminal offence. If he admits that he needs to pay legal fees and pay more, and you don't want to go through complicated judicial procedures, then it's best to mediate privately.