YSK that if you interact with a nice worker in the service industry, calling the company they work for to praise the worker will usually provide a tangible benefit to that person's life. Just don't mention discounts or cut corners.
from /r/YouShouldKnow
YSK認爲，如果你與服務行業的好工人交往，給他們工作的公司打電話表揚該工人，通常會給這個人的生活帶來切實的好處。只是不要提到折扣或偷工減料。