I feel companies should "earn the right" with trials and things. Requiring a credit card which then relies on the end user to remember to cancel if they don't want it is poor form in my opinion (Which gives Spark revenue if the end user forgets because they don't really use it) . I know lots of people do it, but it's not right in my view. Amazon does it, but they have a no questions asked refund policy.
If you have a good product and the user is getting value from it, if it expires at the end of the trial, they will willingly give you their payment details.