check for a message in chatbox which says something like "Oh dear, your dead" or something check it out ur self and if it contains that set a boolean to true and then do the code.
When they send u money it paypal let them say in description " I am paying for what i already recieved " and let them forward u the reciept then give them the script. hope so that helps.
If they scammed u, there is no otherway than you charging back idk other than that sorry i also only use paypal but thinking of changing but idk to which i should change.
After they pay u ask them to forward you the receipt from their's Paypal email address to urs so u would have proof to chargeback later.
And let them go first and type in description "I paid for something which i already received"