I want to buy an event ticket from you, but we're strangers. So I write a contract that releases the money to you once you send the ticket, or vice versa.
ebay has somehow managed to support this use case for something like 20 years on the normal existing banking infrastructure
Yeah, but the idea is that you can eliminate the middleman or implement some as hoc logic that the middleman doesn't support.
The ticket would have to be on the chain and you could then see just how much TicketMaster was making and we can't have that.
Well, the good news is that you could also program event ticketing logic with a blockchain and build a TicketMaster competitor. But now we're venturing outside simple examples :)