Your brain can also get in the way of perceiving the tones properly. I believe a large part of the problem, especially with images that have lots of dark tones, is that the monitor glows, and, even with a good monitor profile, our brains will see these as lighter than they are. I have been fooled many times...
One of the things I always do with dark tones is to use the info palette in Photoshop to see just how bright (or dark) they are. I also like to turn the second info palette readout to LAB mode. This way, the top number you see (the L) reads out lightness and darkness in units from 0 to 100, with 100 being pure white. You can also think of this as a percentage. So when one of my big shadow areas read L 8, I know that's 8% bright---which is really rather dark.
The L readout also interprets colors as humans do, and translates those colors into a meaningful number. If you look at the RGB readout, you get three numbers, many times quite different. The L readout gives you ONE number, corrected for human color perception. Much simpler...
Also, make sure the eyedropper tool option is set to 3x3 sample, or 5x5. "Point sample" reads only one pixel, which can be misleading.
Charlie