Yeah, I checked the credit card contracts here and they allow shops to have minimum transaction amounts (I think they’re required by law to allow this.)
He did mention 4% in his post, too.
If he’s charging that as a flat $ rate, he’s good.
If he’s actually charging 4% and not all of his tenants have the same rent, he might be in a technical violation depending on how you read the agreement.
They could decide to not do business with you in the future, if they decide they’re sick of you. This would not invalidate the VISA terms, because they banned you from the store.