This is probably a silly question but if you use ActiveMerchant (or spree), do the creators of ActiveMerchant (or spree) take a commission? Since it's open source I wouldn't expect them to. But at the same time, because it's such a large undertaking to create a processing gateway, it would not surprise me if they wanted some compensation for their efforts. Or is it simply the case that you only pay a commission to the credit card companies on any payments you receive?
They don't take a commission.