This was the most challenging aspect I experienced when running a company targeting small businesses for four years. About 10% of your clients will be nightmar

This was the most challenging aspect I experienced when running a company targeting small businesses for four years. About 10% of your clients will be nightmares who will hold grudges over relatively small sums of money. No amount of contract language will save you from a user who has made use of the software for two years, decides that they're unsatisfied with it and files chargebacks for every payment made over that time. Sadly, the most rational option is to acquiesce. Even "winning" a chargeback case is a loss, as most payment providers still charge you for the handling of the case and it is a black mark on your account, possibly putting you in danger of losing payment processing ability completely.