As any big collector very well knows, the "estimated value" of an item
is not always what you are going to get for something. About 6 months
ago, my brother and I found some of the first 10 original issues of BONE
at our local comic store all for under 6$. My brother was amazed at his
good fortune, being a fan of Bone and not to mention that the overstreet
price guide priced these at a range between 10-60$ depending on the
issue. When asked about the low pricing, the store owner just answered
that he couldn't sell the stuff.
What my brother failed to understand is that a comic (or any other
collected item) is only as valuable as the market you're trying to sell
to, and in Montreal, Bone just isn't that popular and doesn't sell at
all.
The big catch with all these price guides is that a lot of stores will
price their comics to these standards no matter where they are in the
world. As a result, their pricing is too high on certain items and only
an inexperienced collector would buy them.
That is not to say that price guides are totally evil. As a general rule
they can be quite useful, but they offer a very general estimate on the
value of things, and one has to be careful when buying from a store that
carefully consults the wizard before selling you a comic. It may be a
good idea to look elsewhere first.
All in all, unless you're pricing your comics for your own purposes, for
insurance claims or you're somehow selling them internationally (i.e.
online, mail order), don't rely too heavily on any kind of price guides,
trust your instincts instead.