I'd recommend having trial periods of at least a month and if the user doesn't add a credit card on the trial's end, the account gets demoted to a free severely

I'd recommend having trial periods of at least a month and if the user doesn't add a credit card on the trial's end, the account gets demoted to a free severely limited account. I hate getting locked out of a system and can seriously impact my wanting to stay with the company. Demoting the account gives me an incentive without telling me "hey cheap bastard give me your money or leave!"