Pro Sites removes free level when have a trial?

When I have a trial for a Pro site then the free level is not possible to get?

Even if I ask people on the registration form:
Would you like to upgrade this site to Pro?

Even if they say NO, it creates a trial period of a pro site.

I would like to have the option to sign up for a free site, and if they want to try out a Pro site then have the days of trial.

Shouldn't this be how its supposed to work?