The New Fowler's Modern English Usage has this:
"...theatres, restaurants, and hotels have patrons."
According to my search, I don't see many patrons for
those. I wonder if theatres, restaurants, and hotels
call the users of their services 'customers', 'clients'
or 'guests' also.
'Patrons' are more and more becoming wealthy supporters rather than simple guests or customers. I think it is still common to see in-house notices directed to 'theatre patrons', especially in live theatres. Restaurants now commonly have customers and hotels commonly have guests, though more luxurious examples of both still have patrons, I suspect. Client is better reserved for customers buying expensive products and services (e.g. legal clients) or corporate customers.