As a buyer you ask if the price can be lower than the asking price and the buyer decides. If the answer is "no" then neither buyer nor seller is in any worse position than when they started.
If the buyer's first question is something like "I don't think I can get to your asking price, would you be open to a somewhat lower offer," I imagine that most sellers would not take offense. I know I wouldn't.
The offensive opener, IMO, is asking a seller "what's your best/lowest price." That is insulting to the seller's intelligence because it presumes that the only issue that matters to the buyer is price, and it presumes that the seller is stupid enough to negotiate against himself under those circumstances. In fact, because this is such an insulting approach, it probably works very infrequently -- so the buyer is worse off b/c he likely has missed a chance to have a successful negotation.