The seller did know what he had, but at $180, he let it go for a VERY fair price. Even in poor condition, these usually trade for $250-plus (double with a good original scabbard). In good condition, $4-600. Excellent, $600-plus.
This one is by far and away the best conditioned specimen that I can find pictured on the web.
Nice. A few years ago I traded an MP34 parts kit for a 1918 Au Lion trench knife. I sold the trench knife and now wish that I'd kept it. Pretty cool piece of history.