Does "customer refunds your paid app" mean the customer requests and gets a (full) refund from Apple for a prior app purchase?
(I would say "returns" not "refunds" ... Apple is the one refunding, not the customer. The customer receives the refund. But I guess this is some kind of regional/informal usage I'm not familiar with.)
If so, that's BS. Apple could reasonably keep transaction costs of something like 5%, but the full 30 is crazy.