A good second-hand bookshop rewards patience. Here is how I browse one.
Go without a list
If you go looking for one title, you will probably not find it. Go looking for a surprise instead.
Read the spines, not the covers
Old books often have plain covers. A good title or a publisher you trust is a better guide.
Look in the odd sections
Travel, local history and old cookbooks are where the best finds hide.
Talk to the owner
Tell them the last three books you loved. They know their shelves better than any catalogue.