The other great thing is it doesn't take a lot of time to master. Oh sure, if you want to close multi-million dollar deals it takes some time, but if you just want to learn the basics of closing and how to read people, it's pretty easy.
Also, a lot of these techniques never get old, they're still the same methods people have been using for decades, so it's not like tech where tools and techniques are quickly outdated.
If anybody's interested, I can post some resources.