A discussion about this very topic was had on another forum about the use of toilet plungers.
Dunbar Plumbing stopped using plungers about 7 years ago to protect the customer. Here's why:
Our charges involve correcting a problem with the necessary means that actively took "mechanical means" to assure the problem has been removed.
Countless times we've been called out to replace a leaking wax ring on a toilet wear aggressive plunging was to blame.
To come out and use a plunger can prove offensive to some customers, especially when the charges associated are premium. There is no "full" guarantee that the clog is totally removed with the use of a plunger.
It's hard to call because nothing other than sheer hydronic "jolt" was used that may only of pushed the debris down far enough to allow water movement. Some bets are not always safe ones.
We just feel that between the cost of our time to use that device can have a customer feel robbed by the short visit and no equipment in the drain.