The six tells
One: poreless, waxy skin with no fine lines. Two: perfect bilateral symmetry in a face that was never symmetrical. Three: glassy, over-bright eyes with an unnaturally clean catchlight. Four: hair that ends in a smooth mass rather than individual flyaway strands.
Five: clothing with no fabric weave, wrinkles or thread detail. Six: HDR-style clarity where every part of the image is equally sharp, which no real lens produces.
What realistic output does instead
It keeps texture. Pores, freckles, moles, slight redness and uneven tone are what tell your eye that a surface is skin. It keeps asymmetry — one eyebrow slightly higher, a smile that pulls further to one side.
It also keeps optics: a shallow depth-of-field falloff behind the ears, mild lens vignetting, gentle highlight rolloff and a fine grain structure. Those artefacts are evidence that a physical camera was involved.
How to test a tool in one minute
Upload a photo, generate, then open the result at full size and look only at the cheek and forehead. If they have been smoothed into plastic, the tool is optimising for pretty rather than real, and the result will be spotted.
The second test is the before/after slider: drag it across and watch whether your features move. If the jaw narrows or the nose shortens, the tool generated a new person rather than editing your photo.