I tried very hard to support local bookstores rather than shop on line. Unfortunately the life expectancy of a bookstore within an hour's drive seems to be less than a year whether the store sells new books or second hand.
Part of the problem is that minimum wage clerks aren't necessarily readers--and when they are not, they seem to be completely uninterested in helping readers spend money.
The library is a regular haunt in my life--I make at least 52 visits a year. I also read fantasy and science fiction and buy between 120 and 150 paperbacks every year.
For years I dealt with The Science Fiction shop in NYC. I could call with my monthly order and come the next day the UPS truck would be chug-chugging up the driveway. Unfortunately, they went under.
Now I use Amazon. I don't get a discount on paperbacks there anymore, but my orders generally qualify for free shipping. Further, I figure I owe Amazon some cash money since I research most of my Inter Library Loan Requests through Amazon.
For second hand books, there are two local stores currently struggling and when I want to shop by list rather than by what is on the shelves, I use:
www.pandora.ca/pandora
They specialize in fantasy, science fiction, mysteries and murder--and are very pleasant people to deal with.