So, in light of all the chargeback drama having recently finished on Deviantart, I've decided I want to include a small disclaimer of sorts when I send out an invoice. There's a little box of Terms and Conditions in the Paypal invoice template maker. Problem I'm running into is, how do I make it so that I can protect my backside when someone orders digital goods from me? Like how online games offer special currency that you pay RL money for. I've asked a couple of friends and some seem to think that saying, "By accepting this invoice you agree to acknowledge that the goods you are receiving are digital in nature. Unless an extra fee is paid, you will not receive physical goods," is enough to do so.
But I don't know if it's either a fruitless endeavor or something that I should try to implement. If so, how should I word such a phrase so people understand that they're getting digital goods from me and that they can't issue a chargeback/ask for a refund as per my TOS/disclaimer when they have received the digital goods?