Free Trial before buying stamp packs

I would appreciate having a free trial before buying particular stamp packs. Oftentimes a stamp pack looks good, but when you actually try it out it just doesn't match the standard stamps. A short free trial would be much appreciated! Something like a few days would be enough time for me to figure out if a stamp pack would be a good asset or not. Also, note that it would be handy if you're warned when the free trial expires and it doesn't automatically charge you (or if you can have settings so when the trial is over it doesn't automatically sell you the product if you decide not to have it).