HawthorneVillager.com

Tricky - please note that a lot of people do not say "Free - to a good home" because this can bring out the wacky people; the ones who might use that dog as bait to train guard dogs, the ones who want to breed for puppy mills, the ones who get off on hurting animals...

Many people say "for sale" so they know they are getting a family who is truly interested in the dog for the dog's sake and are willing to commit by paying a few dollars.

We had to send a dog away before and we asked a fee for him for those exact reasons. We wanted to make sure that not only did he go to a good home where he would be loved, but that they also seriously considered it before taking him so that he would not have to be moved again. Once the guy finally decided to take him, we said we didn't want the money, but he insisted on paying for the dog because he was so happy with him. We used to get yearly updates from them thanking us for the dog they were so thrilled with him.
I don't think it's unreasonable and should not be looked at as someone just trading thier friend in for a buck.

I agree
I've heard you should always ask for a considerable amount of money when giving a pet away. This will ensure that the people really are interested in keeping your pet. Many people will take anything for free... Remember your pet can be taken for free or a small amount of money and resold.