You're overreacting OP.
The reason that smoke smell clings to things isn't the smoke, it's the incomplete combustion and soot that sends small particles of oil in the air with the heat. The gases aren't near as bad a problem as the particulate; smoke contains over 3,000 chemicals and many are very good binding agents. The problem wasn't that the seller smoked (at least not for a knife with just steel and Micarta), it was what he smoked. Properly dried tobacco smoke will not generally create the kind of smoke that can be ingrained in material - but wet tobacco and certain brands of cigarettes can. Cheap cigarettes are the worst - another culprit is ash.
For instance, cigarette smoke and wood smoke is much easier to clean than plastic smoke - burning carpet is one reason why house fires will ruin objects that the flames never even get close to.
The good news is, you can usually salvage anything - and a knife that was exposed to cigarette smoke should be easily salvaged. First off, remember that you're dealing with microscopic balls of oil. Wiping it is not a good idea, the first thing you should do is take a Vacuum with HEPA filter and vacuum it (not joking). Get as much of the settled oils that you can off. Then, you should dust it - then clean it with a solvent. I would recommend lemon juice, as it will bind to the oil particles and also cover up some of the smell. Finally, treat it with a fabric spray. The very last step is something someone already mentioned - ozone. Companies like Servpro complete the process of cleaning smoke damage by gathering all the objects in the smallest room it will fit in, closing the door and running an 03 generator (or several) for up to 14 days. I'm not entirely sure of the science (I don't know if the ozone binds and removes or neutralizes the odor particles), but it's by far the fastest and most effective way to get rid of smells. For a building they use a bunch of machines. It will eventually kill the smoke smell on anything. If you don't have access to an ionizer or ozone generator, use other technologies that people have used to clean the air. Charcoal works very well at filtering, and people have been putting baking soda in their refrigerators for a long time. Put a small fan in an enclosed space (smaller the better) with your items and let them set for a few days.
If it was subjected to enough smoke to hold on to the smell, airing it out isn't going to work like you think (you can't just let the smoke breathe out of the material). It isn't a gas you're dealing with, it's the oil and particulate that was deposited in and on the material. What can happen is the oils loose their odor over time.Ventilation will take away odorous particles, and the more that are taken away the less are available for you to smell.
Besides the brand of cigarette and whether it's pipe tobacco or properly dried, it also depends on ventilation of the home, and the habits of the smoker. For example, a smoker that holds their cigarettes as certain way or have bad personal hygeine can start to build up the odor on their hands. It combines with the oil and dirt of their hands (and the ash which retains a lot more oil than the smoke can transport through the air), and when they handle something the odor can end up being much stronger than if they blew smoke directly on the object. With an object like a knife, even the smoker should be able to detect the smell if it was bad enough to hang on during shipping.
You get the best results if you can clean the object before it settles. Usually after 3-7 days it gets a lot harder to clean smoke damage. If you can vacuum the top layer off before it settles you can shorten the time it takes to neutralize the odor by several days.
So 90% of smokers should not have a problem selling knives. A lot of custom knifemakers smoke cigarettes and even worse, cigars - however it is customary when selling something with fabric like curtains, a plush toy, or clothing to note if the home is smoke free. The few that create a problem probably already know it, and should either remedy the situation before they ship an item or make a note of it (if you have a problem when you receive the item, that is definitely something you should leave in feedback).
Good luck OP, but no need to hang smokers over the bad selling practices of one guy.