Yeah that's usually how it works for me. If you offer less the seller goes the other way. Or proceeds to explain that they have buyers lined up at a higher price than my offer already.
I agree with resisting the urge to make a snide comment. Instead of doing that, I posted about it here to get it off my chest.
I purposely don't "allow offers" in my listings because I don't want to encourage people to lowball me. Sometimes someone will message me anyway with an offer and I'll consider it but I honestly want them to pay the asking price and most people do. If you allow offers you're probably going to get them.
The last few times I sold, I did allow offers. I got really lowball offers for a couple of coins. It didn't cost me anything to decline them - except a very little bit of time and attention; I value those highly, but at the volumes I was selling, the burden was negligible.