As all Jiaitai uniforms I've come across have been sparsely badget (and I don't read Japanese) my experience is that it's down to the usual factors:
Feel and quality of the fabric - high cotton content and little or no bleeding of colours in the print.
A deeper olive hue in the green of the pattern, the fakes I've had were a brighter, more 'unnatural' green colour.
Uniform size stamps as well as sown-in tags.
Details in tailoring like pleated back, reinforced elbows and knees , extra material for repairs and extra buttons included (mine are the before-2007 type before velcro apparantly became the norm) and a slender, less BDU style or box-shaped, fit.
Now should abovementioned eBay vendor turn out to be a seller of wellmade fakes, my hat is still off for the quality of the uniform I've got - and he still shipped faster across the globe than any I've ever dealt with before
But I have a question as well; are there two Jiaitai-patterns? It seems like there is a darker, woodland-type pattern and a more yellow, Multicam-type pattern?
In the days after the awful tsunami in north-eastern Japan, TV reports showing the troops deployed to rescue and help, looked very differently clad than parade type images or pictures from Japanese UN missions.