Depends on the situation. Stretch marks do not always signify that someone is fat. In some cases they may have actually lost weight, but because they gained it so quickly in the first place then they were left with the marks. In addition, they may have only gained weight in one area (read: Miss New Booty). Can't completely rule somebody out just because of stretch marks.
stretch marks should be inconsequential unless she got them Eves going on. I know plenty of men who have stretch marks on their shoulders and hips from gaining weight or growing muscles so its not always a signifier of fatness
