I believe 80%+ of a sale is in the buying of the name in the first place - ie best quality at a reasonable price. I don't worry about leaving money on the table as long as the sale price I achieve fits in with my goals. The buyer will probably have skills, patience, experience, contacts, etc (that I don't have) for them to make their profit, and good on them for that.
Have faith in your judgement, after learning as much as you can and making your own decision on the appropriate sale price.
I NEVER appear needy for a sale, even though I might desperately require the money. Repeatedly saying NO to someone who is serious can often get them to move significantly closer to the sale price we want, which we have to determine beforehand. The ones that disappear are simply not serious.
Saying NO to a high price is only difficult if you do not have realistic confidence and faith in what you are asking - I currently have a $65k offer awaiting a reply on one of my names, and will easily be saying NO because I have already had multiple much higher offers for it. (I have already said NO to this particular broker several times about this name and the price has moved upwards from the $50k initial offer.)