Run down a typical detailing service menu and most of the line items involve real cost: ceramic coating product, paint correction compounds and pads, interior extraction chemicals, hours of skilled labor on every single one. Against that backdrop, a finishing fragrance is close to the cheapest thing on the entire list, and it is worth actually comparing the impact per dollar rather than treating it as a rounding error.
A ceramic coating upgrade might run a client several hundred dollars in materials and labor combined, for a result that is genuinely valuable but takes months to visually degrade before anyone notices the investment paid off. A finishing fragrance costs a fraction of that, takes thirty seconds to install, and gets noticed within the first ten seconds of the client sitting back down in the car.
That is not an argument against ceramic coating, or paint correction, or anything else that takes real time and skill. It is an argument for not overlooking the cheapest item on the menu simply because it looks small next to everything else. Impact and cost do not move together in a straight line here, and the fragrance line item badly outperforms its own price tag relative to almost anything else you offer.
If you are looking for the highest return addition to your existing service menu, it is worth starting with the thing that costs the least and gets noticed the fastest, rather than assuming impact only comes from the line items that cost the most to deliver.