Say you bought a nice suit. Can you say shechechiyanu on it if there's a possibility that you might return it.
If you already did say shechichiyanu on it, are you allowed to return it?
In general, one says Shehecheyanu because of the joy one feels - to thank Hashem for allowing us to arrive to that time and feel that joy. Therefore, if you feel joyous after the acquisition of the suit, and it is a piece of clothing with a degree of importance, you should say the blessing (see sources here). If you already know that you might not keep the suit - then better to wait if it mars your joy.
This being said
Of course, don't trust anything you read here and ask your rabbi in real life.