in michigan it is common to see 2 prices at gas stations. a cash price and a credit price. i wonder if this violates visa's rules.
Not anymore since the law changed.
I think it's the same law that got us carry in national parks but I could be wrong.
Retailers Can Offer a Discount for Cash and Check Purchases
Retailers can encourage their customers to use other forms of payment, such as cash and checks, and can discount for PIN debit and cash and checks provided that the offer is made to all respective buyers.
ETA: Got a lot of free time?
You can verify if this is the law that prohibited credit card companies from prohibiting discounts for alternate payments.