Whether to Do Things Properly or Enter as a Tourist

This is for a friend of mine:

Her fiance lives in Brazil (native). She is from the U.S.

He wants to come visit for 3 months and get married.

Now, I did the K-1 Visa thing when I was with my ex. That was 9-10 years ago. So I don't know what has changed. Back then, K-1 Fiance was a lot easier and quicker than a Marriage visa.

I just worry that if he comes for a "visit" and they get married - he will be deported, and they will have to apply for the marriage visa with him in Brazil. Going to Brazil is not an option for her (ex-hub and minor child)

Am I correct?

Thanks :)

Before they go through the horse and pony show with immigration, how do they know each other? How much time have they spent in person together?

Entering as a tourist with the intent to marry is immigration fraud. The consequences of getting caught are severe. He needs to do it the legal way.

Thank you. That is what I thought.