I really doubt that staff in the stores or for that matter, the general populace, have had any instruction on how to protect themselves and others, even how to use/wear a mask properly. They're called cubre-bocas, after all, so wearing them under your nose could seem perfectly logical to some... There's information available but not everyone has internet or TV, or is motivated to find out; I've learned a few things myself that I didn't know, and have had to revise my own strategies as I go along (like with bleach solutions, hot/cold water, shelf-life, how long to leave the solutions on, etc.) because I was doing things all wrong.