Scammers

Alright so I posted an ad on KSL trying to sell my Math Student Solutions book. I got a response! Yay! No not really because this guy is trying to f-ing scam me.
His email: secoface@yahoo.com

He emailed me saying that he is buying this book for his client and that he will give me a check from an authorized dealer for more than what the book is sold for. He said that he'll give me the $25 and $20 extra if I take it off of KSL and mark it as sold because he's a serious buyer. He says that I don't have to worry about shipping because his shipping company will take care of it.
So I talk to many people online and many people don't type with correct punctuation, spelling, etc. but I can spot a foreigner speaking to me. He does not sound like an American. So I marked it as sold but then sent him an email saying that I don't get what he's talking about.
He replies to me: (not in his exact words) I will send you a check from my client for more than the amount that is owed. You have to promise me that you will be trustworthy and take out only what you need then send the rest back to me through Western Union. The shipping will be all taken care of.

Ok, first off, you need money to ship and there's no such thing as having a shipping company take care of things. Maybe to pick up, but not to pack and stuff. Second off, why would you send me a check for more than what the book is worth and make me send it back to you.

So, this is what is going on.

THIS GUY IS SCAMMING ME.

I'm pretty sure he's asking me to cash a check that he stole and send back the cash to him. So pretty much make me do all of the dirty work.

F that.
Although I don't know what to do about it....:/