The screenshot of his conversation with the third party doesn't necessarily prove he was attempting to sell the exact same account. Those stats are rather basic and he could have additional stock or create a new one from scratch as he mentioned.
My concern here is that you're not able to provide screenshots of your conversation with the third party that you claimed tried to sell you the same account. I have a hard time believing someone contacted you and attempted to sell you the same account in the 50 minute time period between RS Master messaging them a price and you then confronting RS Master. This leads me to believe that the third party is you.
Did you reach out to him to set up an agreement for these services to be complete? From what I can gather in the chatlogs, @RS Master was waiting for you to bond the account and provide supplies to the account so he could complete the 14-55 magic, 13-44 prayer and Barrows gloves.

