If I'm looking to buy something off Craigslist, FB Market, etc, I skip any listing that is prematurely aggressive or defensive.
If the item description has any variation of "don't waste my time", I'll skip it even if it's something I really want and the price is good. These people are almost always insufferable pricks.
Half the time their version of "wasting their time" is anything short of your opening message to them being "I'M ON MY WAY WITH CASH IN HAND TO BUY IT NO QUESTIONS ASKED RIGHT NOW!!!".
Also, what's up with people being all aggressive about "I will not respond to 'is this still available'!"
It's not an unreasonable question, people forget to take their listings down all the damn time, and it takes literally one second to type "yes" and hit send.
I've had so many times a listing will even say some version of that and then I message them and they say "it's sold".