Easy job, great for part time
This is an easy job that I would recommend to anyone looking for a relatively easy part time gig. Knowledge and/or like of cars is a plus, but I knew a few people that didn't know much or anything about cars and still did well in the job (one even became a manager).
Hardest part is being nice to every customer, even the ones that get annoyed/angry. Easiest part is being an auto parts store. As a general rule, retail auto parts stores aren't that busy, so it's a pretty laid back job. As long as you do what they ask of you, which isn't that much, everything goes smoothly.