A basic guide to your painted surfaces.
This is a very basic diagram of the layers that exist on newer vehicles. Defects that occur in the clear coat layer (which sits on top of the colour coat) are repairable with compounding and wetsanding, assuming the vehicle hasn’t already received a lot of polishing work in the past which has worked away most of the clear coat already. A well equiped detailer will use a paint depth gauge to see how much clear coat remains so they can decide if it is safe to work on, or how far they can ‘cut’ into the paintwork so that they don’t risk blowing all the way through into the base coat.
As a basic rule, if you can catch your finger nail in the scratch, it probably needs respraying.