Can you take screenshots of the messages sent?
This does look like odd behaviour so his account will probably be marked shortly.
Did he mention the other user who agreed more on a price?
I just asked him for any signed message to make sure he is owner before I can increase my offer
he thought I am a newbie but when I asked for signed message he given false reason that he have another buyer
still I ask him to sign any message with today's date to prove he is real owner of that account from bitcoin address 1LogiCdhcCHYqi1qqfqsnkhxDZ33BaLFLj