Why do so many sellers take offense to offers on their listings?

I have sold quite a few pieces through CAM/USAM and at the bottom of my ad I always state, "please, no trades or low ball offers, those that do will be ignored", and yes, people still email with stupid offers and I just ignore or I will respond if it is truly ridiculous.

What I truly dislike is when people ask, so how much is that in US or Euro funds? Umm, it’s called an "online currency converter" its free and readily available online even...

Just to add, as a Seller I have a set price(ad)and lowest I am willing to accept. If need be, to help my ad along, I will offer "free shipping" in asking price "only" inside my country. It also depends on what I'm selling, a cable is free, a 60 lb amp not so much. If I come down in price during negotiations shipping cost and insurance always plays into it. PayPal fees are always mentioned in the ad and will be charged to the Buyer at going rate, "unless" it is sent as friend/family which is free to the Buyer.

Last, negotiating is always part of the dance, and hopefully all parties leave the floor smiling and with each others phone numbers......

Actually, I do take offense at some low ball offers. Why, we both are smart enough to know what it is worth new and the depreciation value, but yet there are people who "want something for nothing" and I will respond along the lines, you are kidding...right?!