I have a couple of crates full of comics and need to sell, but before that I need to do my research on what I have. What would be the BGG equivalent for comics?
Not really sure, there are a few different "comic book" sites out there where you can enter in your collection.
the one I use is Comicbookrealm.com you can add your comics, the condition you feel that they are in, and it will give you a value. Once you have entered all your comics, it will give you a grand total for your collection.
Each month it will give you an updated value and whether your overall value has increased or decreased.
As for a marketplace on the site, I am not really sure. I haven't done it before. It is difficult to sell an entire collection of comics. Most collectors have a specific comic issue that they are looking for. My own collection is estimated around $8,000. Would I get that? never.