Warped glass top

Before installing this product, check that the glass top is not warped. We've had two delivered to the house, and BOTH of them had a twisted glass top, causing the stovetop to rock back and forth on the counter. One of the tops had more than a 1/4" deviation over the 30" length, and the majority of the defect was in one small area at the corner. It is very obvious, and I have to think that it could lead to the glass breaking unexpectedly. Apparently manufacturing standards are lax, since two stovetops in a row were this far out of whack.