taste it!
seriously, if you can, find a deer farm local...or a small outdoor shop that carries REAL scent from a deer farm. i can smell the difference in the stuff over the store bought stuff...totally different smell...
if you cant find anything local, ordering online would be your next best bet...but the stuff is limited quantity usually and might be hard to find now...most farms that are in the urine business have a way to bring them into estrous a bit early so that they have the stuff ready before the hunters can use it..