Question: MarketPlace Error "You can't message this account"

Hey guy, I have a question regarding this MP error that I've been when I try to contact a specific user on MP. So here is what happens... I saw something I wanted, I reached out to the guy to ask him about it. He replied back to me and when I went to respond I see the message "You can't message this account."... I'm not sure why... and today I tried to contact another person by reaching out to them, and I got the same message, "You cant message this account". When I looked at the guys profile that I messaged today, I see that he has several high-end items posted all over the place. I know they are getting my message because they are replying back... but I am unable to reply to them.

AND... just for giggles, I just tried to message someone else about something unrelated and my message was able to go through and I'm NOT getting the message "you can't message this account"

My only thought is, its spam and MP is blocking them... I'm not suspended or anything, and I'm able to message other people without issues.

Any thoughts..?