Josh, look: I wasn't trying to be insulting, although looking back at my post, I suppose I did exactly that, and I'm sorry. Okay, the guy lied to you - we understand that - but you bought the bike in "as-is" condition. That means as soon as the money changed hands and the bike was in your possession, the other guy had nothing to do with it anymore. He could've poured paint down the cylinder and put sand in the tires, but bottom line, because it was a private sale and not through a dealer, there's not a whole lot you can do about it. I'm sorry you got screwed, but there are a bunch of dishonest people in this world - you just happened to get suckered by one of them.
Your clutch is toast - the shoes are worn down, and no longer contacting the clutch drum, even when you rev it up full throttle. How do I know this? Because my bike did the exact same thing. As soon as I changed clutches, the problem went away. You need to change the clutch.
Use a socket on a short extension to get the center bolt out. If it doesn't come out easily, get a broken screw extractor set, drill the head of the bolt, thread the extractor into the top, and crank that sucker outta there. Get that bad clutch off the bike - use a big screwdriver or crowbar under the bolts, get a gear-puller, even take the entire thing apart and then pry the backing plate off ... just get it off the bike. Order a new clutch (which i'm guessing you already have), set it on the shaft over the keyway, and give it a thunp or two with a rubber mallet to seat it properly. Put a new bolt in the crankshaft, tighten it down, put your clutch cover and chain back on, and go try the bike out.
This is all basic maintenance that you have to do to these bikes to keep them running. Everyone who owns one spends just as much time working on it as they do riding it, so if you plan on keeping it, plan on getting your hands dirty a LOT. As I said earlier, it's your bike - if you want to sell it and throw away all the time and money you've already spent on it, no one here can stop you. Me, I would keep trying to fix it, but it's your choice, not mine.