Merchant fees clarification

[copperglobe]

I've been doing some reading on here and elsewhere. Let me get this straight; there are two sets of fees associated with credit card processing- interchange fees and the merchant fees. The interchange fee is the same no matter who you go with. It's the merchant fee that makes the difference. Am I correct?

 

[MEP001]

AFAIAK the two fees are the merchant processing fee (A percentage of the transaction) and a fixed transaction fee. They both vary. Costco offers merchant processing with no transaction fee which would be very helpful with the many small transactions in car washing.