I would just echo a previous poster concerning looking into the lineage/credentials for the hapkido school and instructor being considered. Hapkido has splintered many times since Choi and I've seen it taught as "tae kwon do with a couple of wrist locks" to "aikido with a couple of kicks". While we may think of aikido as being politically driven at times, there seemed to have been many more splits/dilutions in hapkido.
As with any school, visit the dojang (korean in this case) and see what the classes look like, how the students are treated and the general atmosphere. As far as lineage, etc, I would check out hapkido.com
to learn more about one particular viable federation and my good friend Jere has a nice web page with lots o' hapkido/korean stuff Jere's page
. There are other federations, etc, this is just one that I know a little about.
Good luck with the search.