They should be upfront - advising patrons on entry and not expecting them even to note warnings on a website (even if they are there). But some restauranteurs have no idea how to treat customers.
I went to one that offered a free 'standard' meal if it was your birthday and you were dining with someone else who paid for their meal. When they hit us with a bill for my meal, my husband objected and pointed to the sign promoting their offer. The response was rude and loud - "But she didn't have the 'standard' meal'. I did, but my husband asked for a prawn cocktail as an extra that he would pay for. Because he told them it was for me, they said we hadn't honoured their terms and therefore forfeited the right to the free birthday meal. I wrote a very terse letter to the management telling them I would post complaints and warnings on every public forum I had access to and file a complaint of false advertising. Didn't even get an apology. They went broke a year later. I wonder why?
Another wrote a large tip on their bill, which my husband paid by credit card without noticing the addition (as he, like the rest of us, had enjoyed a few drinks). When I saw the card statement a week later, I lodged a complaint. The response was that they typically expect a large tip and he didn't enter anything so they were entitled to fix his omission. I gave them some free publicity too. And I lodged a formal complaint of fraudulent conduct with our bank which, although it didn't result in any refund, would have loaded them up with some onerous paperwork and stress.
Customer service is not hard, and it pays off. We always write positive reviews of places where the service is good.