Brakes not working right on 1988 Chevy pickup?

I bought the truck from a tire dealer who claims he put $150 into the brakes but when you go to stop it is like when your master cylinder is going out or like you brake pads are wearing out. Since a garage worked on it I am wondering what the problem could be? When you press on the brakes it goes to the floor and you need to press hard. Any answers? Tom