How do you find the value of ET merchandise?

I use Ebay often to establish current market value, as collectable books are often obsolete in their pricing the moment they hit the bookstores. What I do as far as Ebay is concerned is I go to their advanced search, type in what I'm specifically looking for(or you can generalize) and click the box underneath for completed listings and then hit search. The results will be every completed auction for that particular item for the last 30 days, which should give you a good idea of what it is potentially worth.