If You Win An Auction Question

What if you win an auction and the seller vanishes how do you go about concluding the transaction if you can't get any response from the seller? It's really annoying if you have spent a week or more of watching and bidding and finally win only to find that the seller backs out with no response.

 

Thanks for your answer DeluxDon. To give the seller a fair opportunity to respond
How long should a buyer wait before reporting?

 

Thanks for the help Shawn & Don! This information was exactly what I needed!