Painted patches can be very hard to judge with 100% accuracy from pictures, and even in hand it can sometimes be very difficult. That said, this one looks both artificially aged, and to have been painted with modern paints. The modern paint is part of what is giving it a "decal" look, but I doubt it is a decal.
The 23rd Fighter Group is one of the most heavily copied designs, and has been for years. The originals I have seen have been very will executed, many of the fakes not. I am not sure what "crusterized" is, but it does not sound good....which is probably appropriate.
Now this from the standpoint of discussing if the patch is an original from WW II. If someone was buying this as a knock around original jacket, with a very well done postwar patch on it, then it is a pretty nice package. However, it sadly appears from the description, that this guy is hoping that someone bids as if this was right off the pilots back.