Let the chips fall where they may. Sometimes, these big companies talk a lot of shit, and when you call them on it, they fold. We became an approved vendor for a major auto parts company (think O'Reilly's), and they did everything they could to get us to lower our rate. They even told us we could go fuck ourselves, they would get someone else. The next day, they call and tell us we are approved to do every location in the state.
The games these guys play
. When they are bigger than you, they think they can push you around. Thankfully, I do enough advertising and good work. Every time one of them has "taken their ball and gone home" sales still increased that year.
The first rule of business is to have more than one customer. If you don't diversify your customer base, what will you do when they come in and demand a 10% reduction in cost? Beware anyone sending you a contract limiting who you can do business with.