A company called Book Off has identified the needs of this second hand market and is making billions of yen from buying and selling second hand goods. Apart from owning the chain of Book Off stores, they also have a chain of stores that sell used hardware called HARD OFF.
Manga doesn't cost that much (about 400 yen each) but amounts to quite a bit when you are looking for a whole set. I a recently went to Book Off to look for a whole set of manga and took some old magazines in at the same time to see how much they would buy them from me - they paid 100 yen for a few old copies of New Type which was more than expected. Rather than throw out the mags on magazine-recycle day, I now take them into Book Off for the next fellow otaku to enjoy.
Whenever I go to Book Off however, I always see people reading manga from start to finish - they stand there for hours...
I remember selling old manga and idol photo books to a used book store in London many moons ago - they offered me something like 5 pounds for 300 pounds worth of books - didn't want the books because I was moving to Japan anyway so took the cash ^^;
Are there bookstores in your region that buy/sell used Japanese books? Do they buy/sell at a good price?
Also, do you buy second hand stuff? If so, what sort of stuff do you buy?
I'm currently thinking of buying some second hand Mac Minis to set up a server farm.
You probably want to be careful if you buy second hand figures because of what the previous owner may have done to it.