The example is ACME Company has a payment processing system that companies X, Y, and Z can use. It enables more features than just "payment" processing, and it enables more than just "credit card" payments. However, ACME Company wants to avoid adding a surcharge into the model for the customers but needs to charge the Slip Credit Card processing fee and still make a profit. So it wants to charge a 10% fee to the company requesting to use the payment processing function of its service.
So Jon Doe goes to company Z and buys a widget using his credit card for $100 USD. Company Z uses ACME's service, so ACME takes $10 and transfers $90 into the bank account of Company Z. Company Z ships the product.
Somewhere along this beautiful interaction between buyer and seller, ACME company needs to charge that fee. Is that fee legal? Some states prohibit the use of Convenience Fees and Transaction Fees, does that prevent the company to company transactions or is that just buyer to seller.
Many payment processors like Paypal, Stripe, Visa, and Master Card all charge a transaction fee to the business. Therefore the company calculates it's pricing to reflect the cost to the consumer. Generally, consumer's are unaware that Mastercard, Visa, AMEX, Stripe, and PayPal all charge a processing fee. If the consumer new, the consumer would opt for the lowest percentage transaction fee. This is why many of those companies tell business to eat the cost.
My question, in the example provided above, is it lawful for ACME company to charge a 10% fee? If so, legally should it be called a "Transaction Fee" or a "Service Fee?" If not, does that mean all those fees from Mastercard, Visa, AMEX, Stripe, and PayPal are illegal? (in some states and countries)