Condensation should be visible when the sun shines on the container.
I try to keep them pretty moist. In winter this is rarely an issue. In my zone they stay frozen most of the time. It's in spring that you really have to be careful. They can dry quickly in warmer weather.
Well, I find that adding more drainage holes might fix the problem, but not always. My worst containers last year were the deli roasted chicken ones. They are very shallow, soil depth not much more than an inch, and just never seemed to drain adequately. I kept poking holes and slits to no avail. They still stayed mucky. This drove me to research factors affecting drainage in potted plants, and I found that the problem was most likely lack of adequate soil depth. This causes essentially the entire soil to be at the perched water table and there is not enough gravitational pull to drain it.