The listed values for Pets are the MINIMUM values.
Features of a Pet, such as: color, eyes, hair, pattern, etc. may affect the worth of a pet. Some pets are worth more than the value listed.
Be aware of fake custom pet traders. Pet codes will never be offered at any link for free. And a real pet code trade would not require either person to go first. The safe method of trading for a pet code is agreeing upon an offer then telling the person with the code to make the pet the way you want, and trading normally in-game.