The 3M scratch removal system, yes it's a little bit pricy but it really does work and well.
First step is to sand the scratched area with the 3000 grit abrasive square included.
Second, add some rubbing compound from the packet to the purple compounding pad attached to your drill. Swirl the compound into the scratch with the drill running (Velcro drill bit adapter is included)
Third, using the black polishing pad with some scratch remover paste swirl it through the scratch again using your drill.
Last step is to polish the area with a soft clean rag.
Here are the results on a fairly deep scratch, tested on a 2010 Dark Grey Corolla.
95% of the scratch has completely disappeared. Although if you look really closely the deepest part of the scratch (just to the bottom of the door handle) is still slightly visible. Although that area was extremely deep. I did also try the same 3M scratch removal system on surface scratches and I was 100% satisfied, after the buffing I couldn't see the scratches, they had completely disappeared.
My first use of the 3M scratch removal system on a dark blue coloured Honda paint turned out a better result, even the deep scratches on that colour disappeared. Either way this is an excellent scratch removal system. The results will vary depending on the colour and manufacturer of the paint.
Overall I think that this is the best scratch removal system out there for the general public. I give it a 9/10 for as close to a perfect product as one can possible buy at the local automotive store. The main disadvantage is it's price between $25 and $30, it's not cheap compared to the competition.
Oh and in case anyone from 3M is reading this, a little more scratch remover product in the package would be nice.