This is just silly. I understand their frustration but while it's intended to deter people who aren't intending to buy instore it could also deter genuine shoppers. Personally I simply would not buy from a store with this policy.
The whole point of trying something on is so that you can see how something looks and fits before you commit to buying. Who wants to waste $50 on something they may not end up buying or feel forced to buy something ill-fitting or unflattering because they've paid to try it on?
What if you try something on and it doesn't fit and they don't have your size? Or if you try it on and it doesn't look how you thought it would on the hanger (hasn't that happened to everyone?)?