I usually don't tell fake or good (then I'm never wrong;) ). But I don't think I would buy this one. I haven't heard of fake guards badges but it wouldn't surprise me. The real ones start from, I think, 11-12$ and up in Russia (or I have very poor contacts...).
If you like it - buy it. It's the stuff you don't get you will remember for all times.... but good guards badges aren't like order of victory... I'm sure you can find better ones.
I believe this badge is a genuine WWII issue, and is one of the many variations that exist. Sloppy letters and details are not very unusual. They are not very rare and you can certainly find a better looking specimen.
Looks OK to me, except for the screwpost and the screwplate.
That Guards patch is what is known as an aggressor patch. It was used by allied armies on exercises and was worn by "opposition armies" who were dressed as the enemy (usually Soviets) in copied uniforms. The uniforms are very crude (usually poor copies of the KLMK camo one piece smock. This would ahve been worn on a field uniform of some description. They were produced in America as far as I know.
Last saturday I came accross a really poorly made officer cockade which had a double loop and pin attachment which is typically British. I can only assume that this too was an "agressor" item.