I don't know if you all have noticed or not but jet boats aren't exactly bringing in top dollar, it's more like bottom dollar. You spend 20K and are lucky to sell it for 10K. I sold my '71 Rogers for less than the trailer it sat on was worth! (I'd rather see it rebuilt than at the dump, which I was very near doing.) As marcsrollin knows, a mutual friend of ours dumped off a jet boat hull at the dump about a year ago and it cost my friend $45 to dump it, he then sold the trailer for $250 in less than 8 hours, and he didn't get one phone call for the boat and the trailer for $200. You don't build/rebuild an old jet boat for the resale value.
The guy probably just sold the boat cheap and the buyer just wanted the engine.