Before taking any vigalante action, think about a couple of things:
1) We don't know who "Detective" is, other than an anonymous poster on the 'Buzz, or whether his motives are sincere
2) We don't know how current the address info in a DMV database is or if the guy that ripped off has moved a few times since he got his tags, and
3) We don't know if the guy that ripped off the boat owned the vehicle that was traced - its possible that the thief borrowed a buddy's vehicle to go sell the boat.
Right now the lawmen should have enough to go on to bust the guy. Leave it to the pros, if the person listed above is indeed the thief, it'll al be public record eventually.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse