Whatever the advanced sales associate at the kiosk offers you.
Sometimes fastpasses, sometimes gift cards, sometimes nothing. Depends on where you are staying and how hard it is for them to get you to tour (some people don't need any incentive), your level of interest, and if you've toured before. Sometimes special offers are left in your room if you're staying on property that you have to bring with you to tour. There's a DVC forum on here where this and other similar questions about touring get asked.