EBAY PAYPAL ISSUES newbie

i am newbie on ebay,

i am selling Safe Digital Product so shipping by message code/serial key and stuff like that,
if someone even after receiving their article launches a complaint how do i do it? knowing that there is no tracking number for a parcel shipment nor anything seen that it is an electronic delivery ... therefore paypal blocks the money.
how to sell digital things on ebay without having payment / complaint problem?

thanks
regard