Implement a plugin such as cosmicpvp's plugin which would make a user confirm his/her purchase of a rank or key. This would help prevent players purchasing say 1 Legendary Key on OpPvp for a well known player which he/she has a grudge against, and using the charge back feature to return the keys resulting in the ban of the player. With the feature added it will help prevent this sort of scam by making the player confirm the purchase and if they don't the key will not be added to the account and the player hints forth cannot be ban from the server. I am currently unaware where to obtain the plugin, but I believe someone on mc-markets coding section can easily make a plugin that can do great!
