I’d do another smell test after the windows have been up for at least a day. As someone who’s purchased a previous smoker’s car, you cannot remove the smell, it gets everywhere, not just on exposed surfaces. It’ll be in the upholstery, behind the dash, behind panels, in the ventilation system, everywhere. So if you detect any odor on your test, it’ll be something you’ll have to decide, whether it’s something with which you are willing to live. It’ll fade over the years but park in a sunny spot, it’ll be back. So your odor check is important and if there’s any question pass on it and await a car without any smell. Do not believe anyone, especially a sales person, that says they can remove smoking odors. I don’t know about vaping but I think the odors are very much less that that from smokers and it wouldn’t surprise me if there is no residual odor. The nicotine or THC or whatever was used was in a purified form so may well not have that raw smoke stench. Still if someone vaped in the car they may have smoked or allowed others to smoke, so there may be smoking odors. You’ll have to check. Residues: you won’t see them, you can only smell. Do check the ash trays, they’ll often have evidence if they’ve been used for cigarettes. They should be clean an shiny. Hepa filters will remove particles and possibly smells from outside the car but that’s not the problem. BTW, your cell phone usually has a flashlight option so can work in a pinch to look under a seat.
We bought a used Volvo over eBay, sight unseen, but we did pay for a remote mechanic’s evaluation. He didn’t report the cigarette stench. The car was shipped cross country so when it arrived it was ours. It reeked. We cleaned all surfaces, put a fan in with windows down for months, sprayed Fabreeze, and I we even put an ozone generator in there. There was less, but when you are competing with heavy smoking, windows up, for years, there’s a layer of tar inside the car, getting rid of all of it is hopeless. A non smoker’s nose is very sensitive to odors. You can try to remove smoking smells, pay for commercial cleaning, try to cover it up with various scent releasing car mirror dangly things, but if a smoker has smoked regularly in it, that tar is part of the car. I’d love for someone to tell me I’m wrong, I missed something and there is a way to return it to a nonsmokers status. i don’t think I’ll believe them I’ll need to be convinced. For right now a smoker’s car will always be a smoker’s car and I’ll be damned if I’ll ever buy another one.
And if you ever hire a mechanic to go over a car you are considering buying, find out if that mechanic is a smoker. If so, he won’t report cigarette odors. And if I was doing it again, I’d eat the cost, buy the plane tickets, and have a smell for myself. I wish I’d done that with that stinking Volvo.