Hi Blanche,
I'm new to this forum, but have been vaping over 2 years. On another forum, I have frequently read people post that they need 36 mg. Some eventually lowered to 24, some don't. It was totally inappropriate for that vendor to toss your 36mg and sell you his 18mg. !! Now if you'd told him you were vaping 60mg or higher, he could have indicated that amount would seem a bit too high. 36mg is not "pure poison." He is uneducated in that regard.
I generally vape 18 to 24 mg regular 100%VG nic based e-liquids. 36 seems strong for me, but there are those that need that much, it depends on the person and what they are used to in smoking cigarettes. I buy some ready-made and I also DIY.
I also use naturally extracted tobacco's from a couple suppliers and, in addition, I supplement with something called Whole Tobacco Alkaloids (WTA's for short.) from 2 suppliers currently, and will be trying a 3rd (new vendor) to see if what he sells are Nets or WTAs.
Welcome to the journey. That's what I've been calling it. My quit 2 packs a day and started vaping e-cigs journey lol:)