I stumbled upon this video containing a great discussion about comic book values. The discussion is a couple years old but the points are still valid. It’s a great primer for what is important for a comic book value, what comic books are NOT valuable (even though their owners think they are), as well as several other important topics. Jason brings in a CGC representative to offer some opinions, something you don’t get access to every day.
One of the best parts is the discussion about modern comics and how quickly they lose their value. If you are selling your comics or even an advanced collector/investor I highly recommend watching this discussion.