After 40+ years eating in restaurants out here I have a very keen sense of whether or not the service/food quality is up to par.
Condition of restrooms
Tables not bussed
Number/type of customers.
Number/type of servers.
Appearance of cooks
How fast food comes up on the warmers, how quickly it gets picked up by the srrver
I set a timer on my phone. If I don't get greeted within 5 minutes/ order taken within a few minutes more they are on probation. Timing on drink /salad another indicator.
Many ways to see if the organization is competent.
Have walked out many times leaving enough money for the drink so I don't get accused of theft, which is extremely unlikely.