I think it boils down to how much experience you have with archery and whether you can do all your own work. The problem with EBay and other places on the net is that often times it's the inexperienced that use them and end up with ill-fitting equipment because of lack of experience.
They never reach their potential for accuracy and don't know why. Only time they go to a local shop is for service, begrudge paying for it, and walk away with very little knowledge gained.

I say that for those who have the knowledge and can do their own work it's fine. You should know exactly what you are looking for. But then a lot of times it's those with the know-how that patronize local shops for most stuff because in doing so they can keep up with the newest and learn more. Of course, cameraderie may be a part of it, too.