Some gigs offer an object, have I to pay for shipping?
What kind of gig are you buying? And no, if someone is selling you something the shipping should be included. But I would suggest you send a message to the seller BEFORE you buy anything.
Also, be careful. It is technically against the Terms of Service for either the buyer or seller to give out their personal contact information. Some gigs do require certain things, so be sure that this is a legitimate gig.