It all depends on what they're using and at what strength.

Usually those places will be using quite a harsh mix which they do to make sure it's going to get the car 'looking' clean as the customer leaves - that's their only priority. The downside of that is that yes, it's more than likely stripping off the wax or any other protection on the car.

Best off getting some and doing it yourself, then it can mixed at the correct strength to preserve your wax or sealant. Hand pump dispensors are great for applying TFRs.

As above, a good snow foam used regularly is a better bet than to keep using TFR (we must have been typing our replies at the same time lol!)