The waist on a woman that got lipo is very telling and is noticeably different compared to a woman who achieve a flat waist from diet and exercise.
You can also tell some of these women have a surgeon create fake abs on their stomach because the abdominal "muscles" never change appearance when the abs are contracted etc.
I know a girl that has naturally thick thighs, got lipo went from a 6-7 to a 8-9 over night and it's hard to tell she got lipo done. Another way to tell is to look at their pictures growing up, if there was a drastic change in their body especially in a short period of time, it's plastic surgery.