Bubble tips usually don't have much of a problem attaching, and once they're attached, it's really difficult to get them unattached, so if the person you bought it from really yanked it off the rock, more than likely, the foot was damaged (and it sounds like that's what happened). I try to buy my anemones attached to a rock, it saves the ripped foot factor a lot of the time. It's no guarantee that they'll stay on that rock once in your tank, but at least you don't have someone who doesn't know what they're doing ripping its foot apart. I actually ended up with two BTA's because the one I wanted was attached to a rock with another smaller one, so I just took both. My RBTA is attached to a rock that it's been with since it was collected (I actually know the diver that collected it). It moves around the rock, but it's food is so far embedded inside the rock that I wouldn't dare try to pull it off that rock, even thought it's ugly and wish I didn't have that rock in the tank! Haha
If I can't get an anemone already attached to a rock, I try to find one that is attached to glass. Then you know the foot is capable of attaching to something. When they're in the sand, it's hard to really tell. Small tears usually can repair themselves, but with the stress of moving into a new tank, etc, it makes it less likely that they will. And when they try to attach to a rock, it sometimes can make the tear worse.