I know someone who works in my local PAH, and she is a lovely person who works in a rescue on her weekends, but I wouldnt ask them for nutrition advice, and there isn't many people I see in the store that I would ask. Mind you, I dont ask my vet either, as she feeds Whiskas and Hills.
Mark, when I had Tom and Ginger at teh weight clinic, they were quite happy that I was feeding both of them mainly wet, as my vet rarely recommends prescription diets.