Student or Learner
1)"you can tell what someone's interior motives REALLY are by the subtle clues they give you, so subtle are these clues that they're most often overlooked" - I guess the closest I could find was 'wolf in sheep's clothing', but I wanted something somewhat more specific...as in, you can tell their true motives by signs you may overlook...
2) Someone who complains about something AFTER the fact, as in, Bob decides to complain about the messy house right before the guests arrive, why couldn't Bob have said something beforehand?
There is a great little reference right here on-site. https://www.usingenglish.com/reference/idioms/
For the second one..."armchair general" might work well. That's not in the list, but my grandpa used to be fond of calling my grandma that one.