Gumroad says its flat fee is 10%, but I doubt that

Sounds like a lesson learned on understanding payment processing fees before launching a product. If your business model is dependent on low-value, high volume transactions, you have to research providers where the fee structure is better than the standard credit card charges.

Gumroad was dishonest to us on so many levels. Fortunately, it was around the time Stripe became available in our country, so we could move our 'toys' to a new payment processor (I know Gumroad is also a marketplace, but that was irrelevant for us).