Somebody from this number once they give us a check for more than the item you're selling and then wants us to send them a check back seems odd doesn't it.
Its way beyond odd. Its fraud. And its old as dirt.
The way the scam works, the buyer gives you a paper check that you are to deposit in your account. You are to wire part of that money to a shipper selected by the buyer. Your wired money transfer clears instantly. The buyer's check bounces, but it may take 2 weeks or more. You owe your bank the full amount of the paper check, including the shipping fee you have already sent to someone else. You also owe your bank a fee for depositing a bad check and you may be in trouble with the law for passing a bad check.