Bargaining, mercantile savvy, barter, bigger and better deal. . .for some shop keepers, it's how the deal is made that keeps them in business and not the money.
Not really been to PI several times. Dad retired there and has a Filipino wife. The touristy spots are horrible and expensive, but you get away from the Westernized and chain places, I found it to be great.
I am continuing to learn, so there is that. I am not a know-it-all or a keyboard warrior.