This thread has some good ideas, including some suggestions direct from Flow. It might be worth trying some of them:
It can be. My bees filled the end cells, but if you have ever done traditional beekeeping, you will see that even in an all wax honey super, the outer cells around the edge of the frame may not be filled or capped. The second photo in this blog shows what I mean:
http://www.personal.psu.edu/jad52/blogs/bee_log/2009/08/
I would try some of the ideas in the link above first. However, if you really can’t inspect them, I would harvest cautiously.
If the frame isn’t fully capped, you risk a big honey leak into the hive from the uncapped cell faces. Drowned bees are not pretty. To help reduce this, you might open the frame in 20% segments, waiting 10 minutes before you advance the key to the next segment. If you see bees pouring out of the front of the hive, or honey dripping from the back of the hive, you will know that you shouldn’t continue opening any more cells. In that case, if the nectar flow is over for the year, I would use a bee escape below the super to clear it of bees, then take it inside the house and harvest over a large cookie sheet to act as a drip tray.
As you won’t know if the honey is capped, you also can’t be sure it is ripe. So I would buy a cheap honey refractometer to test the honey. They are simple to use, and then you know whether you can sell it as honey (less than 18.6% water), or whether it should be kept in the freezer and used quickly once defrosted. 