Thats unfortunate, ive bought almost exclusively used aquariums and have never had one crack on me in my years in the hobby. I have bought new aquariums that had their flaws though so you never know. You simply had a case of bad luck so you will see it as you see it. Tank used or new are made to last, I know a few people who have had the same tank running for over 10yrs.

Is that a Biocube or Red sea max? The curved corner made me ask? 1st time ive seen a crack in one there. It looks as if it was bumped into something some time ago and weakend it and when you set it up the pressure finally gave way to that crack.