How can I set up a financial credit card payment?

Hi,

I want to set up a shopping website, I want users to pay me monthly. It depends on the chosen service plan.

For example, if the user bought item A for $1500, the user can choose how many months they want to pay it. how can I make sure that the user will not cheat it, and stick to the contract? Because I'm afraid that I may go to bankruptcy if they cheat it.

They might cheat their credit cards right? How does the bank protect the online shops from this kind of theft?