Deposit system for my website

The deposit system could be a normal payment system and not necessarily a direct deposit that will be able to let users perform the following actions: 1- users can sell other users points with any currency e.g. 5000 pts for 20 USD. 2- once a user sold something, my website should take a fee of lets say 5 percent. 3- the sale process is only from users to users. I don't mind if a freelancer propose an affiliation with another website (including ecommerce, stores etc...) so things can be more secure and then do the necessary adaptation on my website. I am also open to other suggestions that guarantee a secure operation for this process. Also freelancers are free to ask me which script (in case of any) i should buy for them so they can use it to complete the job.