Wow! It sounds like the listing agent could be guilty of a number of ethical violations. But as my mother in law used to say, you point a finger and you point three back at yourself.
Aside from whatever the other agent did, you are making rookie mistakes that can land you in hot water. I recommend you team up with a mentor and familiarize yourself with NAR's Code of Ethics and Standards of Practice. You should start with ARTICLE 1, it talks about pledging yourself to promote and protect the interests of your client. Move on to ARTICLE 9, it says in plain english, words to the affect of, Realtors will get it in writing. ARTICLE 11 discusses a Realtor's reasonable expected competence. If I were a cash buyer dropping a half million bucks, I'd expect nothing less. Please take this a constructive criticism moving forward. Good luck.