How is this best done?
Get out and go to those who claim to know some things. Don't go to just one guy. go to several. Some are just starting out, some are just starting to teach, some may be on the net on fishing expeditions searching for information and pretending to have a depth of skill or knowledge they really don't have.
Talk is cheap
A good bet is to ask them..."Where are your students or people you have taught for more than just the recent year or two?" And see what they come up with.
On another level who cares what someone knows it's whether they can replicate it in you. Everyone who has been in the arts a long time has met guys who spin the B.S. and /or guys who are talented but cannot replicate their skills. The chief concern for someone looking is to learn. So who has proof they can teach what they know. See If they know something worth learning and whether they have the ability to teach!. If it isn't replicable and they cannot present anyone...be careful. And never settle for what one single guy tells you, no matter who it is.
I tell people to never settle for the self professed amateurs here either. Everyone who has trained with me goes out to train with Master level teachers in various arts; Daito ryu, Aikido, ICMA, and other various people or methods so they can think for themselves. You need to find out whats out there and who's got what. No one can judge for you. Only you can, You'll know who you want to train with