We just recently bought and sold a Subaru that had been heavily smoked in by multiple teens and it STUNK! We took an ozone generator from a hot tub and hooked a computer fan to it for air flow.
Day 1. Very noticable difference
Day 2. Almost gone
Day 3. Smelled like a fresh spring rain!
Day 7. Ozonator had been out of car since day 3 and there was a faint smell if smoke and body odor. Started the car and turned on the A/C and whew! The A/C, especially when set to max, will circulate all odors over the evaporator and since it is wet with condensate, it is a stench sponge.
Re-introduce ozonator with car running and A/C set to max for 3 hours. No more stench.
Day22. Still no stench-sold car.