Free samples have been proven to be a waste of time. You need to take a supplement on a consistent basis to tell if it works. Just "trying" something once or twice isn't going to tell you anything.
It would be like taking a couple of dianabol for a few days. You won;t feel anything but that doesn't mean it isn't effective.
ANd as mentioned, it you're unsatisfied with a product you get your money back. Can't beat that.