I agree. Unfortunately, sometimes people don't store their Chanel bags properly (such as stacking them) and this crease can form without the bag ever being worn. That might have been what happened with this bag causing a crease in the bottom while the rest of the bag is in excellent condition. I agree, it would have been nice if they pointed it out, but it does clearly appear in a few pictures and it doesn't look like they tried to hide it.Even though the seller did not specifically state that the bottom is bent, one of the pictures clearly shows that there are creases and bends on the bottom side of the bag.
Creases like this will usually straighten up if stored firmly stuffed with the bottom of the bag pressed against the wall of their storage box, however, the signs of the crease may never fully go away. This is a tough situation because the bag isn't mint condition as stated, but this flaw was clearly pictured. If this is a flaw that would bother you, you should have seen it and refrained from bidding. Pictures speak a thousand words, way more than you can expect most sellers to put in their listings! Because of that it's hard to say the bag isn't as pictured. You may have some luck with SNAD but it's a tough call. If you absolutely can't live with the bag, go ahead and try. However, if I were you, I'd take the $200, stuff the bag and love it!