The car came out spotless, so why was the smell back a week later?

Why does the smell come back?

Smoke does not stay in the air: it settles into the fabric, the seat foam, the carpet and the headliner. A product that only treats the air lasts as long as the product does, and heat and humidity bring the smell back. You have to treat the places the smell stays:

• the headliner holds a lot of smell and is easy to ruin: work it with as little moisture as you can and no pressure, because if it gets soaked the glue lets go and it stains, creases or sags;
• in seats and carpet, the smell is in the foam under the fabric: extract the product you put in rather than leaving the material soaked, because an interior left damp for long picks up a damp smell;
• the cabin filter has spent months catching smoke: replace it as part of the job and treat the ventilation ducts, or the smell comes back as soon as the fan runs.

Enzymes, fragrance or ozone?

An enzyme treatment works on the organic matter that produces the smell; a fragrance or air freshener only covers it. Fragrance belongs at the end, in a car already treated; used as the fix, the smell comes back, and so does the client, the following week. Ozone is a breathing hazard: use it with the car empty, air the car out before anyone gets in, and follow the times and doses in your generator's manual.

What about the cars that never get back to zero?

Some cars never lose the smell, such as those smoked in every day for years. Say so in the quote, before you take the job, and charge for the work you will actually do. On your next odour job:

• before you give a price, get into the car after it has been closed up and smell it;
• check the cabin filter and put the replacement in the price;
• a week after handover, call the client and ask whether the smell has come back.