Over in my small town, there are big players, corporates, midsize companies, small fish, m&p's, the whole range. Those big big fish, the ones that have to keep moving, they can be fun to work with, but as the joke goes, why are lawyers safe to swim in shark infested waters? Professional courtesy. They can be great, and they can be a royal PITA. Staff migrate from smaller firms to larger ones, and sometimes, they get to bring along suppliers who they trust.
All jobs get quoted to cover for Rumsfeldian uncertainties, but where the customer is on a real tight budget, if I've come in way under on shop time, And if the client is a decent human being, I'll pass on a little of the savings. Not everyone chooses to maximise profit at any cost. Customers never expect the job to come in under quote, but what goes around sometimes is returned, one way or another.