I know some of my stuff is going to be posted on tube sites eventually and I post free previews often. The only thing I ask is if you do post my stuff anywhere at least post the clip store link or jwties.com with it. Then at least people know where they can get more like it and I can find it and get feedback. But you will notice I have been watermarking my previews lately in case this becomes hard for you guys to remember.
It can't be prevented. I'd recommend to include the addy to the store throughout the video, not too large but readable at the bottom of the clip, so it's always there but doesn't get in the way. That way it becomes free advertising....
I feel for you "Tickled guy"! a few years back my ex and i started a little site on clips for sale, only to find some moron posted them all for free on youtube.