Other ways would be analogous. I can't think of any way to do this in a hypothetical lab situation such that it's not vulnerable to my criticism. Can you?
What you could do is look at actual data (for concert tickets, plane tickets, train tickets, etc) and see if complimentary increases in ticket quality really correspond to increased purchases in the future. You might also be able to rig up an exit survey with objective questions like "do you regret your ticket purchase" and "would you recommend us to your friends" and compare the answers given by regular ticketholders and those given by ticketholders given a complimentary increase in ticket quality. But, again, that wouldn't work in a lab setting.
What you could do is look at actual data (for concert tickets, plane tickets, train tickets, etc) and see if complimentary increases in ticket quality really correspond to increased purchases in the future. You might also be able to rig up an exit survey with objective questions like "do you regret your ticket purchase" and "would you recommend us to your friends" and compare the answers given by regular ticketholders and those given by ticketholders given a complimentary increase in ticket quality. But, again, that wouldn't work in a lab setting.