To, me, it's not an obvious fake, and I'd spend $5 or so just to get it and do the research. What bothers me about it is that it looks like it's been glued down to the piece of paper. It's not a piece of the original cover so I'm guessing it is cut from an old album.
The best reference for US locals is Larry Lyon's (expensive) three-volume set "The Identifier for Carriers, Locals, Fakes, Forgeries and Bogus Posts of the United States." This looks like a genuine Type VIII example of this stamp, 20L13. It could possibly be a reprint (requires close examination under magnification to be sure).