.
It is called courtesy.
No, it is called negotiation.
if someone asks you your bottom line and you give it to them, then don't bother offering lower because it is the bottom line.
That's not the way the way the real world works. When you give your bottom line you may be firm, but a lot of people respond with a price higher than they are ultimately willing to take. Since I don't have any idea whether you are firm or not I have to offer lower to find out. Again, it is called a negotiation.
If you are so easily offended then don't negotiate. Say so in the first place and list it firm then ignore anything below your price. Once you open the door to a negotiation it is ridiculous to get "offended" at an offer, any offer.
.