List Out The Jewellery I Need To Know If This Is A Scam Or Illegal, Please Help....?

I need to know if this is a scam or illegal, please help....? - list out the jewellery

I have tried to sell jewelry on Craig's List, and I have like 4 people who want to buy and then tell him to send me extra money and the price I ask deduct and send the rest of Western Union. To send a wire transfer or check. Is this fraud to? Is this an illegal way, if I do that. In order to cash the money and send the rest of the money via Western Union?
Why are these different people that this and why. I would really like to know.
I hope you can help me.