Your friend has no idea what he's talking about. Leaving wax residue doesn't cause burn marks in paint, that's just insane. Sealant does not burn through clear coat and accusing the guy of that prob set him off because it's just crazy.
I don't get what you mean by dents, my guess is this is just a visual trick due to unevenness in the wax.
Can you take some pics in sunlight so we can see? Prob just needs a good polish and wax.