If you want to be certain that your boots are leaking, take Kinkyboots advice, thats what I always do to my leaking boots and I've managed to buy a few pairs that leak over the past ten years. I place them on top of our wheely bin in daylight and fill both boots with water, then wait a while and then take photographs of each side and the top toe areas. My photos easily show where my boots have leaked. I then empty them and place the boots upside down on our washing line, they soon dry out.
If you are confident that they leak just take them back, I've never had a problem in getting a refund or just choosing new boots.