Furthermore, what incentive does a couple about to get married have for joining the platform? It sounds like they are somewhat locked into the vendors that come to them. I think you mention that they can cancel but then there is then no incentive for the couple to take it seriously. It turns into quote shopping instead of an actual marketplace.
I like the idea because this space is ripe for change. There is a lot of money flowing around and people who get married are confused about where is the best/most affordable/most reputable place to put it. I think if you can align the incentives on both side properly, this could be a real winner.