I doubt this guy is a basket thief, but a Google search of his phone number reveals numerous Craigslist postings. My guess is that he's RE-selling stuff that he's bought cheap from other people -- some of which may very well be stolen.
It's a little hard to follow the guy's writing, but it sounds like he's selling the top and middle of a basket, with NO POLE. So, to be more specific, have any courses recently had their baskets stripped down to nothing but the central pole?
It wouldn't be a bad idea to braze the three main pieces together. Anyone can cut a nut off a bolt, even if they've been made hard to wrench apart by rounding the bolt heads and nuts. Zinc is a good flux for bronze and it wouldn't be hard to sweat a little brazing rod into each joint. This could be done on the spot with an oxy/acetylene torch. If the whole basket got lifted, the bronze job would be an identifier.
The Corporate Empire is NOT a Constitutional Republic...
...but it plays one on TV.
You can pick up a quick set of steel stamps, grab hammer and said stamps and stamp the steel with whatever you want to identify the baskets. We do this at work all the time to stamp HIN numbers on boats.