deal in something—trade in a particular commodity:
- Before shops were common in every village, he dealt in needles, thread, and the like.
deal with something—
1. be a customer of a business:
- I’ve dealt with this firm for twenty years.
2. manage smth.; attend to smth.:
- There are many difficulties to be dealt with when starting a business.
3. (of a book, etc.) be concerned with smth.; treat a subject:
- His latest book deals with police methods.