Does your house smell like a dog?  Are his "gifts" still in the yard?  Do you have a dead fish floating in the aquarium?  Do you have a cat door that allows her to bring "prizes" into the living room?  Is cat litter spilling out of a smelly litter box?  Do you have an iguana, pet spider, or hamster baking in the sun by the window? 

ALL of these are pet issues I have personally run into while showing houses.  These are a huge turn-off to buyers, and should be considered a "DON'T" when trying to sell a house!!!!

If you want to make a best first-impression, banish all evidence of your family pets.