1995 Buick Century Brake fluid flush

Varied opinions my view.

What color is the fluid? Black or clear?

First off, it certainly won't hurt. But do you need it?
Probably not.

Will it make your brakes last longer?

I would love to hear that explaination. Based on the fact that they say it will get rid of rust, says that person is a salesman more than anything. If it is so bad that there is rust in the system, there would be some serious problems. Which I highly doubt are present.

What brakes service are they doing and how much to flush?