I agree with the OP that you accomplish nothing by insulting the seller and that insulting the seller can prevent the buyer from making a deal. That seems to be the OP's point if I read the original post correctly.
The OP does not exactly define what a "low ball" offer is so I can only assume. Is a "low ball" offer one that is x% below asking price? Is it x% below retail price? Is it x% below wholesale price? Is it a price that could/would/might insult the seller? Is it an price offered to intentionally intimidate the seller? I'm not really sure.
When dealing with buying and selling stuff, there are basically 4 prices types:
#1. Motivated buyer price (typically the asking price)
#2. Patient informed buyer price (typically a less than the asking price)
#3. Patient informed seller price (asking price or reasonably close to it)
#4. Motivated seller price (much less than prices #1, #2, or #3)
I personally have partaken in all 4 price types. I mostly buy and sell in price ranges #2 and #3. As a rule I try to avoid #1. However, I will often look for #4 prices when purchasing big ticket items when possible.
Examples of my experience with these price types include:
#1. My truck broke down on the interstate 4 hours from home with a failed catylic converter.
#2. Buying something online that I'm not in a hurry to get
#3. Sold our first house during a seller's market
#4. Sold our 5th wheel camper that had some issues and I wanted it gone quickly without much hassle
When I sold our 5th wheel camper, I sold it for almost nothing. We had lived in the camper for over a decade and were ready to end that phase of our lives. We just wanted the camper off our property so I would no longer have to look at it or maintain it. Had I been willing to wait and fix a few things on it, I could have sold it for double the price I gave it away for. I sold it to a younger couple who was building a house and wanted to live on-site while building just as we did. I was ecstatic at selling the camper, even at a "low ball" price. It was a win-win. I openly disclosed all the issues to the buyer but knew our final price was low enough to more than compensate for the issues.
Some people seem to think that selling something at a low price automatically means that someone got taken advantage of. Some people seem to think that buying something at a low price and selling it for a profit is somehow unethical (don't ever trade in your car at a dealer's lot if you feel this way because that's what all car dealer's do). Some people seem to think that obtaining a bargain price means that somebody loses and somebody else wins. I don't necessarily believe any of these things.
Selling something at 50% of retail price can be a win-win for both parties. There's more to valuing an item than just the selling price, such as hassle factor, urgency, etc. With all these intangibles involved, it is really tough to know if your price is a "low ball". Anybody in business for themselves must commonly buy low (materials and/or labor) or they will not stay in business long, especially during a slow market. That's just a fact. Someone who doesn't understand this reality is a bit naive in my opinion.
Regarding insulting the seller, I don't spent too much time worrying about that. I won't intentionally insult someone. However, many people don't really understand how quickly items bought at retail prices depreciate in value by just removing the item off the lot or out of the store. They don't understand that their new $3000 dining room set lost 50% of its resell price the day it left the store. So when you offer them a reasonable price of $1000 three years later they get "insulted". I can't predict or control other people's emotions so I just offer up to the amount the item is worth to me based the price and availability of similar items and how badly or quickly I need the item. If the person gets insulted, I've done nothing immoral or unethical. I'm not trying to get over on them. Some people carry their feelings on their shoulders and I'm not going to lose sleep if it happens.
