I have these two lovelies for sale in the shop. As you can see the cane in the bottom photo is quite bowed, stretched, sagging or whatever you call it. I accidentally figured out a solution to this problem. It's really easy in fact. I actually just bought a steamer (it's awesome---I insist that everyone get one of these) and was cleaning the chairs with it and after the cane dried, it tightened right back up. There is no more sagging at all. I realize that lots of people don't have a steamer (but you should, you really should!) so I'm wondering if it would work if you moistened the cane with hot water (and really, I bet it was just the moisture that did this rather than the heat) using a wash cloth and let it dry that it might not tighten back up. Try it and let me know!
I just picked these up today. I love them and totally want them for my house. But of course they are for sale. It might be a bit before I list them--one of them needs some of the cane fixed. But if you're interested, let me know.