You and Mr Bitbay first sign the contract stating what ticket Mr Bitbay is receiving and how much he'll be paying you for it. You also define how much collateral money you put in the smart contract.  

You both put the collateral money into the contract and the contract is locked.

You send Mr Bitbay his tickets, Mr Bitbay sends you his money. Once you both have what you want, you use your personal key to unlock the contract and the collateral money is released back to you.

In case you or Mr Bitbay don't receive what they signed up for, one or both of you won't use their key to unlock the contract. The collateral money remains in there either indefinitely or until the defined period of time runs out and the money burns up. OR of course, until you both find a way to settle it. Either through extending the contract, building a new one or simply holding up your side of the deal.