David Bebbington is right to say that many clients have a formula in mind, and they all want the same darn thing, and this can get tedious. I found this to be the case when I was shooting performers' headshots for a while.
There are many tricks that can be done with lighting, posing, camera position, retouching and things like soft lenses. You can make a face look thinner with short lighting, or you can make a thin face look fuller with broad lighting, for instance, or you can use a high camera angle to de-emphasize a flabby neck or double chin. Many of these issues, though, are things you might not notice, but that the subject is self-conscious about, so you've got to figure out what their own body issues are.
It's worth noting that classic portraitists like Karsh and Hurrell later in his career didn't use soft lenses. They used sharp lenses and smoothed things out with pencil on the neg. Hurrell even preferred that his subjects not wear foundation makeup--only eye makeup and lipstick--so that he could capture the glow from clean skin and retouch the blemishes later.