You definitely shouldn't be accepting payments without a way for someone to get in touch to say "hey you're overcharging me / double charging me / I want my money back"

If your service is free than I don't think anyone is entitled to customer support, since there aren't really customers in the first place

On this we totally agree, but I don't see that distinction made in GP or GGP comments so just wanted to note that this isn't a full reinforcement of GGP comment