Fiancé visa is not designed to be "try before you buy" with 90 day return of fiancé back to their country if something doesn't work out.
Expectation is you are sure you want to get married, before you file for K-1.
There is a reason you write and sign letter of intent to marry.
Treating people like objects or goods is inhumane. Many of K-1 leave everything behind in their home country: relatives, friends, job, environment they know, language, place they live etc etc.