"There are many vintage bass and guitar listings, some listed multiple times for ridiculous prices"
And same item's auction ending at different times, item supposedly located in different places: looks very hinky to me.
As the old saying goes, "if it looks too good to be true..."
Whoever wrote the descriptions either knows something about stringed instruments or copied the descriptions elsewhere.
If those items/auctions were for real, there would be reasonable "bidding starts at" prices listed, IMHO.
Look at the feedback: I only scanned a few pages quickly, but most items are knickknacks and geegaws, mostly selling for less than $30 and very few for over $50. Even if you want to assume that that much of it is legit, that still constitutes a red flag. I didn't spot a single musical instrument supposedly having been sold.
If they can get enough people to say, "what they heck" and send $15-$20 on a whim, that still could add up to some money.
I'll bet that the seller disappears from eBay within a week.
Guess we'll see...