Yup...instantly know trying to dip deeper into their customers pocket with that fuel flush quote...
Brake fluid is hydroscpic...meaning it will absorb it out of the air and should be flushed at each pad or shoe charge...or every 2-3 tears. Color is one key indicator...it will darken as it absorbs moisture. I don't recommend ever top up the brake MC reservoir...it is a good indicator of fluid level...
If you are into keeping the fluids "fresh"...flush the diff fluid too...and...the most ignored fluid...the power steering fluid...
PS...the newer OATs and HOATs MUST be flushed per the manual recommendation...ruination of the system much higher than with American Green coolant