why does all the paint have to come off?

 

the body shop said if i want the discount i must remove all the paint so its easier for them to paint it..

im planning to sand off the paint and bring it to the bodyshop but does anyone know what kind of grid sand paper should i use?

 

It's tough to say without actually being able to see it, but based on this I'd try wet sanding it with 220 grit then step it down to 400 and finish it with 600. You need to find that sweet spot where the paint comes off but doesn't gouge up the plastic too bad.