If its a chick..what size bra do you wear? Is a great question.
..but seriously, knowing nicotine and ohms law can be the most important for a shop as well as knowing what are safe batteries and what are junk.
If i walk into a shop and buy a mech mod and the person behind the counter tried to sell me an efest 35 amp battery and tells me i can use it down to .2 with a fancy coil then ill walk out empty handed pretty much and would never recommend them to anyone new to vaping who doesnt know any better.
Knowing batteries is as important as ohms law and knowing nic levels...There are really only a handful of recommended batteries for use in most all mods...If its not made by SONY, SAMSUNG OR LG then is probably a re wrap with false advertising on it that can give your shop a bad reputation.
Nic levels i can give an example for..Customer walks in and says they are new to vaping and want a subohm set up...you sell them say a kanger subox mini kit...they need juice now....The last customer that walked in bought a kanger evod starter kit and bought some 18mg juice...So is this the same nic level you would try to sell to the customer buying the subohm kit?..hope not.
There is alot of different circumstances to making a decision for someone..Ultimately you want a return customer who trusts in your sales persons/management judgement.
Maybe send these possible managers here to VU and we can give them a shake down and see who would better fit the position.
In all honesty you should know these things as well being the owner...just sayin