There are a few ways processors charge for credit card acceptance. Here we have provided a brief overview of those methods. Each card brand (Visa, MasterCard, Discover, AmEx) charges a percentage of the transaction, a per transaction fee, or both for a business to accept their cards. This is called interchange. The rate you are eligible for depends on your business.

This is the most common method card processors used historically and even today. Processors markup interchange by a number of basis points and/or a few extra cents per transaction then pass that rate to the merchant. This can be the lowest cost for your business because it allows customization by card brand since each card type has a different interchange. 

Flat rate processing has recently become prevalent due to companies like Square, Clover, Toast, etc. offering it as a simple solution to a complex industry. However, its simplicity is exactly why it isn't necessarily the best option. The rates these companies give merchants are, by nature of running a business, higher than interchange. Because each brand's interchange differs, they charge a rate greater than the highest interchange (it's always AmEx). 

Surcharging has seen a rise in usage among smaller merchants because it can eliminate one of their operating costs entirely. With surcharging, merchants add a fee, typically 3% to credit card transactions. This can incentivise customers to pay cash, while allowing the business to keep more of their profits. There are a few limitations of this practice. You must accept an alternate form of payment if you want to use surcharging, and you cannot surcharge tips.