for their foolishness

I can't say that I understand the situation, but the sentence is correct.

Vincent -- you have been posting a whole story one sentence at a time in separate posts. Did you see my reply yesterday, where I suggested that it's hard to understand the individual sentences without any context? It would be better if you posted a whole paragraph in one post.

Oh, I saw the threads just now. Thanks your advice. Next time , I would post a whole text. Thanks!!

I don't know much about the nitty-gritties of the words but can a person be deemed as foolish if they have been tricked?

transitive verb
1 :to deceive by cunning or artifice : impose on, defraud, or cheat usually by specious means : affect or induce by deceit or trickery trick another in a sale* *trick him into consent
2 : to obtain or bring about by

If you are a victim of a trick, you may have been cheated and may feel foolish and upset. You just asked a good question. I've been wanting to learn the word for a long time but have to say it's not as easy as it sounds. I mean I've heard it many times but still don't know how to use it in the right situation. Shame on me.

You shouldn't feel ashamed. It takes an awful lot of time and effort to learn any language, espcially English, which I think is one of most constantly evolving languages with it's users being so diversed and it's ubiquitous spread and application.

PBF