What do you do when a place you had no trouble at before suddenly has sour milk every time? Do you complain or wait it out?

I'd stop buying any product that is consistently bad and stick to products that are packaged or canned with a long shelf life. I wouldn't bother to complain as i would assume they are on it or don't care..

Don't complain, but tell the owner/manager about it. That way they can notify the company they purchased the milk from, get credit, and restock the shelves with milk that is not only safe for you to consume, but safe for all the other customers that buy milk from that establishment.

I would not keep going to a place that has sour milk more than once.

milk has pus and dead bacteria in it, not good for you, it's a reminder not to drink that garbage......it's ok from the cow, but not ok after they pasteurize it......you need to read more....