Almost every cleaning company sells a deep clean, and almost none of them will tell you what is in it. That vagueness is the problem, because the gap between a thorough regular clean and a genuine deep clean is about three hours of work and a completely different list.
A regular clean maintains what is already there. Surfaces get wiped, floors get vacuumed and mopped, bathrooms get scrubbed, trash goes out. It is the right service for a house that is already at a good baseline, and it is not supposed to reach much further than that.
A deep clean is what gets you to that baseline in the first place. In the kitchen it means the inside of the oven and refrigerator, the range hood filter, the grease film on cabinet fronts, and behind and under the appliances where it is safe to pull them out. In bathrooms it means grout lines, hard water on shower glass and fixtures, the seal where tile meets tub, and the underside of the toilet base that nobody enjoys mentioning.
Everywhere else, a deep clean is mostly about the surfaces people forget are surfaces: the tops of door frames, baseboards hand-wiped rather than vacuumed, switch plates, air vents, window sills and tracks, ceiling fan blades, and the inside of light fixtures where a startling amount of dust collects.
The order matters as much as the list. A deep clean works from the ceiling down and finishes floors last, because anything else means cleaning the floor twice or, more likely, cleaning it once and then dropping dust on it.
So when you get a quote, ask for the list. A company that deep cleans for a living can produce a room-by-room breakdown in about a minute. If the answer is just a price and the word thorough, you are probably buying a long regular clean at a deep clean rate.