It is definitely NOT an original board - or any version I've ever seen, and I have 5 or 6 various ones laying around
It is mounted to a cocktail/cabaret 4-board-style plate (though it too differs from original), and as another user noted, it appears to be missing at least the audio board. Upon closer examination, it is evident that this board never had a seperate audio board, and the various harness connectors are in different locations, as well as the dipswitch bank. Note the lack of Nintendo copyrights, or any TKG lettering on the board as well, nor are there any socketed eproms on the shown side of the board (and all 4 DK original boards have eproms on them).
In short, it is a bootleg. But they do say it works, so $50 isn't bad per se, just noone else will probably ever want it from you