To me it's all in the delivery. If you present your reasonable offer in a manner that is respectful, then typically sellers won't be offended.
this all day long. Perosnally I just cant make myself pay someones asking price without trying first so i generally always make an offer lower than asking price but i try to stay within reason (generally 10-15%) less than what they were asking, then if its too low they then say what they could do it for. It seems to me a big part is less people want to haggle which is half the fun to me.