Originally I thought the same thing: that he was buying stuff to gain what he was missing in a collection, and then reselling what he didn't need. Then, I recalled the storage unit for a Kodak DCS-1, which rang a bell with that eBay ID. Sure enough, he's the one that bought that cheap and then has tried twice to sell it off for about 2x what he paid for it.
I then called up his 30-day bidding history alongside his 30-day selling history, and see several such items. When I looked at what he bought vs. what he was selling, I see where those items seem to be the same with a much better description and set of photos. So, I formulated a new thought.
Now, it may well be that he's getting stuff to find that what he already has is better and then re-selling it. That's certainly possible. Looking at the rate that's he's buying and selling stuff, though, makes me think that it's probable that he's working the old buy-n-sell auction angle.
Not that it matters. Either way, it looks like he's having fun.