I have always gotten great feedback when I do a shoot and the owners pets are in the shot. It comes from two sides. First the owner loves seeing their most favorite animal having its picture take and then for the world to see them on the fact sheets and web. The situation reinforces your relationship with the owner by showing affection to a member of their family. This all falls into keeping the seller happy.
Then the other side, are the potential buyers. 39% of U.S. households own at least one dog and 34 % of U.S. households own at least one cat.* Then consider the people that love animals but due to allergies or rental restrictions cannot have one, or people that just like to see cute, fluffy, small creatures and you end up with a lot of animal lovers in our country.
When you shoot, take a number of shots, animals like to move around a lot. Then pick the best one.
Animals add life, happiness and a softness that an empty room cannot provide, showing that a wonderful life was being had in this home and you (the buyer) can have the same.
Just make sure the animals are seen and not smelt.
* www.hsus.org, The Humane Society's web site