I just checked and I have a similar message in small font at the bottom of my sent messages too, so it's normal & nothing to worry about. I can't see how it could possibly put your account at risk if all you were doing was asking routine sorts of questions.
It is very unusual not to get any reply from 3 separate sellers. In my experience, 99.9% of sellers respond within 24 hours.
I'm not sure when you messaged them, but remember, not everyone is on a phone or checking 24/7 so give them reasonable time.
If you don't hear back within, say, 48 hours, just move on & look at other items from other sellers.
