The check they send you, which is for more than your asking price, is meant to cover the fee for thair shipper. It's a lie.
You deposit the check, send the "extra" to the alleged shipper, and "keep" the rest for your item.
Problem is, days after you've sent off the payment to the shipper and maybe spent some of the rest from that check, the check will be returned as fake.
It's been going on for a long time. Google CRAIGS LIST SCAM and stay away from deals like this. Deal in cash only.