Last year I worked for X, a hat-trading company
or
Last year I worked for X, a hat trading company
For some reason I was inclined to go with the hyphenated version, which now seems wrong, but I'd like to be sure.
Last year I worked for X, a hat-trading company
or
Last year I worked for X, a hat trading company
For some reason I was inclined to go with the hyphenated version, which now seems wrong, but I'd like to be sure.
Either one is fine, but I would go with the hyphen to link hat and trading together as a modifier of company. In your case, though, hat trading company makes perfect sense, as you are talking about a trading company that specializes in hats. The choice may depend on the context, e.g., on whether you are emphasizing company as part of a comparison of one type of company to another. – Richard Kayser