I can tell when my wife has gained weight when she tells me. Otherwise, she just looks beautiful. Conversely, she looks even MORE beautiful when she's lost weight. Although mostly that's because she has this wonderful smile after she's done so, and she can get into those pants that have been hanging in the closet for five years.
OTOH, I'm worthless for fashion assessment. "How do these look on me?" "Great, honey!" "Now how about these?" "Even better!" "And these?" "Super!" "How's this look?" "Best of all!" "This is the first set I tried on. Why do I even ask you?" I have no idea. I'm totally sincere but utterly useless, alas.