If your subfloor isn't flat, forget about a good carpet install
I've seen too many jobs where the carpet looks bad after a few months. The reason is always the same: the subfloor wasn't prepared right. Lumps and dips show through, and seams come apart. Take the time to level it properly, or you'll regret it. Last week, I fixed a DIY job where the homeowner skipped this step. The carpet was already stretching and bubbling. Do it right the first time, or don't do it at all.
How could anyone hide a dip in the foundation? That's not a small cosmetic fix. The whole floor plane is off, it throws everything out of level. A pro might smooth over a tiny hairline crack in the drywall, but an actual dip in the slab? That's impossible to hide, it would be obvious the second you put a level on it or tried to lay flooring. What they can do is fix it properly, but hiding it? No way.