Do you think this is fraud activity?

I posted a household item on cragslist and asked $1000. The original price for this item was about $3000. It was made 7 years ago, but seldom used and in a very good condition. I got about 11 offers only one day after posting. 7 of the buyers are willing to pay the asking price or higher. Two of the buyers told me they would pay by bank certified check. They said they would mail me a check one is $3400 (another said $2700) to me. They told me to deduct the amount for the item and then transfer the left to their shipper via Western union. The item I want to sell is used not new. Why they want to pay so much? Do you think this is fraud activity? Sorry, I can't input Chinese in this computer.