OK, let me help you out here:
First, it's not unissued, it is almost certainly a russian "dip blue" capture. These are almost all truly pieces captured on the eastern front, checked out thouroughly, then reblued over the old blueing in a process known as "hot dipping" which is sort of like a real durable cold blue. Then they were put in storage and kept until being surplused off in the late 90's.
Yours is an "AC" code, which stands for Walther production, and is dated 43. I'll bet all the serials match, most seem to.
$550 is near the top end for a Russian dip P-38, but they are steadily climbing in value. A really, truly unissued AC-43 would set you back.....oh, say a grand or even a little more. Accuracy in the P-38 can vary from "pretty dang decent" to " 6 inch groups at 10 feet". Really, shooting it wont hurt it and it seems a shame not to at least try it out.