How should I decide whether to buy used or buy new, especially for intro level classes where textbooks are used for more than one sem
Not only that, you can choose to rent new or used!
I don’t think it really matters if you buy new or used, as long as it is the correct edition that the professor is using (e.g., if you do homework from the 10th edition, it may be different than the 11th edition.
What is better? Saving money or a pristine book? THat is up to you.
As far as renting, if you are taking a two semester course or if it is a foundation course for your major, I would buy. If it is something that you will take once and have no further classes in, then I would rent. For example, if you were taking the Beatles FSP with its 13 books, it may make sense to rent. But for Calc 1, it may make sense to buy so you have it for future reference.