We do not impose any additional charges. The $1 that you saw is only put on hold and will be automatically released back to you after a few days.
Because you used your credit card to sign up for a free trial our payment processor has no way to check if the card is legit without pretending to charge you a tiny amount. So they put a hold on a small fee as a way to run an authorization check but of course you will not be charged this fee in the end.
You’ll be able to verify that no actual payment has been made with your credit card company as well.