Not to sound mean here, but this forum is basically doing all the work for you, perhaps we should just all pool our money and outright buy the tunic for you.
As you will see from the replies that have kindly been provided by various forum members, the questions YOU should be asking of the vendor are:
history of the tunic, ie, who had it;
when was it made (an image of the manufacture's stamp); and
better views of the insignia.
These are just starter questions, then there are the unique details of the tunic and the insignia in which YOU need to analize in order for YOU to decide it you want to spend your money on this item.
As it is, right now some person is asking you to fork over 400+ dollars for something you seem to have no idea what you are buying or what you should be looking for in order to make an informed decision on the purchase. Does that not worry you? It is all well and good that you are interested in collecting this sort of material, but if your plan is just to keep finding things and then asking the forum if the material is worth buying, well, you might want to re-evaluate you collecting model.
Ask the questions of the vendor and tell us what you have learned.