> I think it's up to the customer to decide how the use the purchased product or service, since when do you owe an explanation to a vendor where or how their product will be used?

It goes both ways. The vendor can also decide they don't want to deal with a customer who's being intentionally dishonest with them.

It's quite simple for them to just refund your deposit/money and leave you without a florist a week before your wedding, especially since you didn't sign the type of two-way "binding" (I'm using that term loosely here) agreement that you do with a wedding.

I spoke to several vendors in the course of my research who handled situations like that in exactly that manner, for what it's worth. In one case the vendor arrived at the venue on the day-of, realized it was a wedding, and straight up just turned around and went home. Another basically required a "security deposit" that would be returned once the vendor confirmed the event wasn't actually a wedding.