Giving discounts for locals without tipping off tourists
Hawaii, California, or Maine: it doesn't matter where you are. Merchants will find a way to gouge the tourists while not making enemies with the locals. Some of them are more obvious than others.
I haven't witnessed the Hawaii version of this personally, but a few people have told me that using your driver license when buying ordinary goods and services is a great way to get a discount. It sounds like one of those things which perhaps I shouldn't have heard, since it will just make the tourists angry when they find out. I got the impression that it is otherwise not advertised.
When I visited Maine earlier this year, it was pretty obvious. A couple of places came right out and posted signs offering pretty good discounts for people with in-state IDs. I saw it vary between 10% and 20% in my travels. One place in particular was just a snack stand up on top of a rocky place, but its location made it very popular. Their scheme sounds just like the Hawaii one, only they make it known that they're doing it.
Then there's one of my local haunts which makes pizza here in town. Every time you order from them, you get a colorful little sheet of paper which informs you that your next medium or large pizza is $2 off. They give these out without fail whether you eat there in the restaurant or take it out. At first I thought they were being nice, but it's just a standard thing they do.
What this does in practice is zap the people from out of town who obviously have no way to already have a coupon on them. Only those rare individuals who will visit that pizza place twice in the same trip could benefit from it. Meanwhile, all of the locals should have figured this out and probably have one or two coupons in their purse or wallet just ready for the next visit.
It's subtle, but it does seem to work. There's also the fact that seeing a coupon in your pocket or on the fridge might make you choose a given place over another, all things being equal. It might just be enough to tip your decision-making in their favor for that meal.