A forced free trial is a direct-marketing technique, usually for goods sold by regular subscription, in which potential buyers are sent a number of free samples of a product, usually periodic publications.
It is said that announcing a three-issue free trial and sending out a fourth issue works well to ensure good subscription rates. There are several places in which free trials can be found. Free trials are used by many different companies offering products and services. It is a marketing & advertising move in which the company or maker of said product or service is so confident in their offering that they give it to you in a trial test format. Once you make up your mind that you do like the product or service which you tried the company knows they'll have your business.
However a free trial in exchange for credit card details can not be stated as a free trial, as there is a component of expenditure.
There are different websites on the web where you can find specifically forced free trial offers and/or free trial offers.
http://offertrials.com being one of them.