I don't think it's reasonable to expect a particular negotiating etiquette; everyone will bring their own style to the table. It's up to you as a seller to develop a range of responses to meet the range of negotiating styles people have. Which includes gauging how much effort to put into particular conversations, based on whether they're likely to be a dead-end.
Quite a few years ago, I sold a moderate amount of NWT stuff on the forum and it was noticeable just how different people were in discussing price. In those days, I prioritised rapid turnover of items, so would cut my prices aggressively to find the market value that moved the item within the timeframe I wanted. These days, I only occasionally sell used items from my own wardrobe instead, so tolerate a much longer wait and can ask a commensurately higher price as I've no need to turn stock over.
Perhaps I'm just naive, but I don't think anyone's ever set out to deliberately waste my time over those years. It's more that every item has a different value to each person that sees it, and some people are more willing to test the waters even if they haven't fully convinced themselves they actually want the item. I wouldn't view it as annoying or time-wasting; instead, it's an opportunity to present the item in the best light to them and if it's rapidly obvious that you're not in the same ballpark on price, to part amicably (but swiftly) until the next item comes along... or you decide to cut your price.
Getting annoyed over a negotiation is only likely to harm the maximum value you can extract from the negotiation because you'll go on tilt. Zen it out, dude , Zen it out.