As a writer, I also do a lot of reading, and the "bought vs. brought" issue is one I've seen show up too many times in books.
Bought
Bought is the past tense form of "buy" and is used to indicate something was purchased. It means you got something by paying money (or another form of payment) for it.
Brought
Brought is the past tense form of "bring." It's used to indicate something was carried or transported from one location to another.
These two words are not interchangeable.
Example: She bought the groceries and then brought them home.