That is logical speculation about why the seller put the "?" mark there. But I have little doubt you are correct in that assessment. However, I myself have a somewhat strict definition of "faulty." If I sell something that only works when plugged in, and if the buyer cannot plug it in because there is nothing to plug in, then I say it is "faulty" insofar as the buyer cannot use it in the condition in which it was meant to be used. That was my original point and pun about the sellers use of the question mark. But as you may expect, I posted my previous comment with a sense of humor more than anything else, simply because I see a lot of these things on EBAY.
With that said, you Australian auction buyers may get what you want if you buy this HD20. I don't know. But it's your choice. You just need to find a way to plug it in, or otherwise find a use for what you get. And as jongleur properly points out, if you can live with the "fault," then you can get a good price on items like this. Whether or not it then becomes a "good deal" depends on what you can do with it once you have it.