To remove a scratch, there's no other way but to level the surface of the paint all around it down to the level of the scratch.
Things like scratch-X are "compounding" liquids, and if you apply it correctly, it gently levels the surface around the scratch as you rub it in. My guess is wet sand is when they use a sander. I've seen TSXs sanded well (post-sanding pictures), I believe it's all about the skill.
Maybe ask to see some of the work of these pro-detailing people, and talk to them to better understand the technique they will apply.