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.
If a vendor who supplies kids' entertainment rental (like those blow-up house things) tried to charge more for their services at a wedding than at a birthday party, I'd think they were trying to gouge. Flowers, something I know very little about, I could understand being treated differently for a wedding than other events, but I'd be interested in why.
I mean, you can just ask why if you're curious. Most of them are sole proprietorships. It's not like you're dealing with a large corporation where pricing is set by a corporate office.
Re: bailing, honestly I think most of them just react negatively to being lied to because there's some element of a personal relationship involved in this kind of service. I'd similarly be pretty pissed if my boss lied to me intentionally about what I was working on.