Very interesting remarks Dan.
You said these two comments in your post:
"If an item is listed for sale at a set price and you are the first to respond, then the item should be yours. I WILL NOT offer more for an item than the seller wants! Why would you? I don't expect people to do this when I am selling an item either."
and:
If you don't know the value of an item and don't take the time to research it then you get whatever you ask for.
I believe you answered my question regarding the ethics of taking advantage of someone that might not know any better. I'm not saying seller did know any better or not in this instance... I was just curious how you felt if they didn't know any better and now believe I know how you feel.