Having sold plenty of items in my life, I am aware that pointing out an item's faults, whether that item is a car, a house, a piece of furniture, etc, is a tried and true negotiating tool used for the purpose of diminishing the value in the eyes of a seller and ultimately bringing the asking price down.
However, there is a fine line between having a courteous and honest discussion about a property's condition and being so obnoxious as to back the seller into a corner to where they feel so "broken" that they must acquiesce against their will.
An example - several years ago when I was living in Phoenix I had my car for sale for $1,000. A guy from the neighborhood made an appointment to see the car, came over, and proceeded to bad-mouth every single aspect of my car. I had kept it impeccably maintained, and I knew it was a good car for the price. Yet this person made me feel so bad, basically saying it was such a crappy car that I would be lucky to get $700 for it. Then he said he wanted it for $700. I reluctantly said "Okay"; inside, I was perplexed because he had just finished telling me in not-so-nice terms that my car was a P.O.S. He arranged to come by in the morning with the cash.
Later on that afternoon, as I was sitting on the porch, this other guy is walking down the street and sees my "For Sale" sign on the car. He stops and talks to me, looks under the hood for a few minutes and says, "This car looks pretty good-no air conditioning for Arizona but I can deal with that, how much do you want for it?" I told him I was asking $1,000 but that I would take $950. He says, "We've got a deal! I'll go get my money". He was back within an hour, we did the paperwork and he took off in his new car.
Guess who's not a happy camper the next morning? The mean guy pounding on my door with $700 asking where his car is. I looked at him and said, "I'm sorry but someone offered me more. Besides, with all of the 'problems' my car had, I'm surprised you still wanted it".
Now, I am expecting to get blasted for that story, because I did not keep my word with the first guy. But to be honest, if the second guy had offered me $700 I would have sold it to him instead because he treated my little car and I with respect.
There's a right way and a wrong way to negotiate. I appreciate that the idea is to not exude any emotional attachment to an item. However, if your idea of negotiating is using a belittling tone and going over the top with disparaging comments about the item you are wanting to purchase, the only thing you will accomplish is to tick me off and make me not want to sell it to you.
When I was selling my business a few years ago, the best thing the selling agent said to me was, "I know you want x, but it's just not worth that much". He said it in an honest, caring tone and he was right. We came back down to reality, sold the business and never looked back. If he would've started bashing the very business that we had worked so hard to create, I would've chosen any alternative to selling it to his buyers. But then that's just me, I'm stubborn that way.