I had issues with vapor initially. It often made me cough. Same happens to many non-vapors who sample my PVs.
Just advise these people that it took them time to adjust to smoking cigarettes (how quickly we all forget those days), and it will take some time to adjust to vapor. It's normal and it will pass.
Insure that they are using the proper inhale technique. NOT directly into the lungs. Take in a small "mouthful". I usually tell non-vapors to imagine sucking on a thick milkshake with a straw. Slow gentle draws into the mouth. They can either now inhale gently into their lungs, or exhale through both their nose and mouth.
Instruct them that it's not necessary to inhale into the lungs to absorb the nicotine in vapor. Being that it is a smaller molecule and different chemical structure, nicotine in vapor is absorbed primarily in the mouth and nose.
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I also tell potential vapors that although it appears to be similar to smoking, it is not. Smoking is easy. Light up and go. If you run out, there's a store 5 minutes aways that sells cigarettes.
Vaping is hard. It takes pre-planning and organizational skills. Preparation of juice delivery devices, charging batteries, planning how much e-liquid to buy and how long it will take to arrive. Enforce the need for backups for everything and why. The initial expense in purchasing a new setup is very shocking to many new vapors. "Why can't I just have one battery and a topper?" Assure them that once they get batteries, charger, juice delivery devices and e-liquid, that subsequent expenses will be far less with only replacement JDD's and additional e-liquid.