CA,
2) it’s simple, if he is unsure he asks Rav Hachshir. He doesn’t just say “Eh”. Even if you believe that is appropriate.
3) I’ve never seen someone just take a head of lettuce or similar and just eat it in the supermarket. The Kosher markets I go to clearly label what’s been washed and checked and what’s not.
You have a problem with assigning your failings to others and therefore you should know that when you make assumptions, while they are accurate about yourself, there is no evidence or even a smidgen of a reason to think they are true about the person you ascribe it to.