I can sell subscriptions, but afraid to code it myself.. what premade systems do i need to know?

hi

i can sell subscriptions on my sites, something along the ever-awesome setup of "pay monthly fee for unlimited access". i am good with php, mysql, linux, and "all in-between", but am afraid to do it on my own cause charging people involves refunds and monthly subscriptions, and i am afraid of cheaters...

what would you recommend? having a "no-refunds" policy? or what? i am not sure. please, advice! =) should i delegate all $$$ related issues to the platform i sell on like fiverr or upwork and such?

is there a respectable step-by-step on this? would be great..