I generally modify store-bought modules to fit my campaign. For instance, I always found "Waterdeep" to be a little too clean cut for my Forgotten Realms campaign. Having grown up in a fairly urban harbor town, I wanted more grit to the City of cities in Faerun. When "Freeport" came out for d20, I bought up as much of it as I could find. The modules have been run in my FR campaign as a sort of dark urban version of Waterdeep, with all references to "Freeport" changed to Waterdeep, all references to the gods changed, the people of Yig changed to Yuan-Ti, etc. For me, that's part of the fun.