Lowball offers can be annoying and some are downright amusing, especially when people just don't seem to be able to read a situation. I have had examples where people have offered me a box of cheap knives plus electrical appliances and what not for a higher-end knife. And it is funny when they do that in a non-Exchange thread where they can see my entire collection and I am clearly not into the type of knives he was offering, even if he offered me a box of them.
My perspective on offers has changed a little for the following reason:
There was a time when I was very active on the exchange and I knew exactly what the knives I was selling or buying were worth. So I listed my prices as firm and I didn't negotiate, except for "forum friends", multiple or repeat purchases etc. I would accept and even offer goodwill discounts without being asked.
But I have not been actively following the exchange for probably two years now. With the current prevalent practice of deleting prices after the sale, I think it is very difficult for occasional sellers to determine a fair price for some items. And things are very cyclical on specific knives. There are times when one thing is the hot thing and they sell for premium but a year later it is something else. I don't want to gouge anybody but also don't want to throw good money away.
So now I try to find as many data points as I can before I list but sometimes you cannot find even a single data point on older or rarer knives and that is when things become harder, and you have to be open to negotiation and to let the market help you determine the price. In those cases however I think, for me at least, that it becomes an emotional rather than a market based decision, e.g. "I paid X and even though the market says it is worth X-100, I am just not willing to sell it for that". Or if someone offers you a price and you look at his other postings and if you see he is a serial lowballer or tire-kicker then again, for emotional reasons, it becomes easier to decline his offer. In such cases I think that it is a little easier to get annoyed by the lowballers but for the occasional buyer that sends you an offer, in good faith, that is much lower than what you expected, it is just a standard part of business and a data point that can help you.