common courtesy ...

If someone does something for you, especially if it's at your request/behest, say, "Thank you." Say, "I appreciate it." Say, "Thank you; I appreciate it."

If you accuse/imply someone of doing something wrong or bad, and then come to find out/realize/see that you were wrong in your judgment, the proper response is to apologize. "I'm sorry I accused you of doing XXXX, or implying you did XXXX. I was wrong and I apologize to you. Please forgive me." Also, "I'm sorry for judging you based on (whatever) and that I didn't talk to you first to hear your side of things. That was wrong of me."

Thanks. I appreciate it.

---