Ask HN: Best way to accept payments without extra transaction fees?

I'm building out an application for a customer-base, where they already accept payments in-person today. I'd like to allow them to accept payments online, but they can't tolerate the extra percentage charge that a service like Stripe adds.

What's the best path forwards for accepting payments online without any fees beyond standard credit card fees? This is for Canada & USA, which may complicate things a bit.