I don't know if you have a web-site or not, but if you don't you should. A guy I once knew in Kansas put up a site that answered almost every question anyone could have and he also put up about 25 photos per car. This takes some time, but so does dealing with tire-kickers over the phone.

His lookie-loo rate dropped off to almost nothing after he set up the site and posted a sign outside saying to check out any car check out his site. If it is on the site is is for sale, if not its' not.

As a part of the sale paperwork he makes a big deal of taking down the ad for the car. The new owner can see that his 'new' car is removed from the site; it is all a part of the selling process. Sort of a 'I know you just bought the car but I am still involved with you' sort of thing. This might help build repeat business or it might not, but the ad for the car has to be taken down anyway so why not do it with the buyer there?

You could also post on the site your asking price and the NADA price and let folks know the price is firm. If the car does not sell then let folks know you will adjust the price and they will know it when it appears on the site.