Feed stores usually have quite a variety of products for the various animals of store clients. It is essential to get acquainted with every food item offered by the store. Of course you have to go to work there before you can learn all this. In the mean time you can study animal nutrition. Try to start your study on the animals most serviced by the store; usually dogs, cats, horses and cattle. For instance dogs that are overweight should be recommended to have a grain-free dog food with more protein or one of the weight control feeds sold by many dog food companies. It goes on from there.
I worked on a farm as a youth. Currently I own two dogs who are getting heavy. I purchased three dog foods that eliminate grains and provide weight control and have just about chosen a winner from them.
I am also going to exercise the dogs more than in the past.