i usually order online from sephora. if you were living in the states, they'd even cover the RETURN SHIPPING cost for you. or of course you could just bring it back into a store and return it there.
one time my order came and the item was damaged in the shipment. they covered the return shipping for me too. which was about $15cad.~ sephora probably has the best customer service in the cosmetics field ga la
I think they would let you exchange for something else, if 你有ALLERGY loh...
Especially if you exchange for something more expensive or add more items (same brand), they won't "gee-gut" you geh...
not sure about the bay, but i did it once at holts. my skin is between two colors and i chose the darker color first, but then i changed my mine. I went back and exchanged the brand new one for a lighter color. when they typed in my phone#, they had my purchase on file. so you can try try