Do your homework before you buy a CECB. After you do your homework and decide to buy one, don't use the coupon on the initial purchase. First purchase without using your coupon and try the box out. If after all your homework and you like it after trying it, then you take it back to the retailer for a refund and repurchase using your coupon.
Make sure your retailer will accept returns on the CECB if a coupon is not used. Most retailers allow you 30 days from the date of purchase for returns on electronics.