Well, sure, but having the customer flash a card to the employee would save more time than having the customer hand over the card for inspection by an employee.
...but it would invite a secondary market for these cards. The logistics of fabricating them would suck, and you have to look at an ID to judge if a card should offered anyway.
Plus having special cards feels corporate, not homey. Looking at an ID for locals discount is pretty well trodden ground.
> but it would invite a secondary market for these cards
There are already markets for fake IDs, so unless you're suggesting that small local restaurants purchase scanners to confirm the authenticity of each ID, it would be relatively easy to circumvent this check too. (Some states require IDs to be scanned for selling alcohol, but many, e.g. in Oregon, do not, and the only check is some employee looking at a card in their hands for a couple of seconds)
> Plus having special cards feels corporate
Not at all. Plenty of local restaurants in my are (Portland, OR) have rewards cards, where you get stamps and a free meal after some amount of stamps.
The high prices would be to ward off these one-time customers who are only there for the single instagram photo. If someone is invested enough to make a fake ID just for cheaper burgers, presumably they're going to be repeat customers that develop a relationship with the restaurant, which is what he wants.
The point is, there are ways to distinguish between locals and non-locals. There are merits and drawbacks to having your own ID card vs. using a state ID card.