Expo Collision Center

I went to expo collision center to freshen up my car including the cracks on my rear bumper. They gave me an estimate with an entire rear bumper replacement.When I dropped off the car, I asked them to keep my old rear bumper on the side so I can pick it up with the car after it was done. He immediately went on the defensive mode and said "Why do you need it, you don't need it". I obviously wanted my old rear bumper back because I want to make sure the I actually got a new one from him.They literally called me back 5 minutes later and tell me that they can patch up my old bumper so I wouldn't need a new one. A sound very suspicious doesn't it? Then they said that it'll save me $50 if I did it that way. I agreed to it and he sent me a second estimate with only $20 off with even more suspicious body work quotes.I called them the very next morning so I can go through the 2nd estimate with them. They got on the defense mode again and literally started yelling at me.