Complex sentence: Cars may be second or third depending on the context of the question-in matters of travel, the third may be used, in matters pertaining to the value of the car, or of buying or selling a car, then the second may be used.
Split into simpler sentences: Cars may be second or third depending on the context of the question. In matters of travel or consideration of their use, the third may be used, in matters pertaining to the value of the car, or of buying or selling a car, then the second may be used.