This commonly happens when a guest visits a new/different location that may be owned by a different franchise. While the Brand Name may be the same (Rudy's Really Good Eats) each franchise -- Rudy's Really Good Eats - Las Vegas or Rudy's Really Good Eats - Austin will have their own merchant service id that will be unique to their location(s) that they own.
In its most specific use, merchant services usually refers to merchant processing services that enables a business to accept a transaction payment through a secure (encrypted) channel using the customer's credit card or debit card.