Herman,
Lets take your senario of "Got something you want to get around $1,500 for? List it at $1,700 and include free Paypal and ground shipping"
So you list it at $1700.00. And lets say that this item has (recently) sold on Agon before for $1500.00 to $1700.00. You get an offer of $500.00 to include shipping and Paypal. This is approximately the OP's 75% off of asking price (which is where he thinks lowballing kicks in).
What would you do?
Do you think he is really going to even come close to your $1500.00 by negotiating with him? I don't get offended, but I also won't give this person even one minute of my time to respond.