I would definately wait for one that is attached and has sticky tenticles and responds to food. If the not attaching is just due to shipping stress, have the store hold it for a few days. I doubt this is a healthy anemone, but time will tell. You probably want a positive ID too as lighting conditions needed and clown hosting probability is dependant on the anemone. True and false percs are not naturaly symbiotic with BTAs, but maroons are.