I do buy on-line from stores where I know that their sizing suits and fits me. Only been let down once in several years.
I did buy a gorgeous-looking dress from an unknown on-line firm. It was mid-calf length, with splits over a fairly see-though underskirt. When it arrived - yes it was gorgeous, but the model was (I had omitted to notice) a smallish Asian lady and I am 5'8". Yes, I can wear it - but the translucent bits are mid-thigh on me! I've worn it twice, with great success - but I have to pick my audience because I am not far off 70! Caution is advised and quality is definitely 'wear a few times'. :)