As new ads are placed or as old ads are bumped, your ad will progressively fall lower in placement. A bump credit can be used to bring your ad back to the top of the list of ads for your breed. It also will bring your ad to the top of all dog for sale ads but don't expect to be there long!
BTW, if you have a standard ad you will be bumped to the front of the standard ads group. You will not go all the way to the top of your breed group. That area is available for Featured ads.
You can't win if you don't play the game -- Me!
All cruelty springs from weakness -- Seneca
Sometimes a dog is as good as any man -- Bell/Houser