Upwork: This website offers a great marketplace for selling just about any professional service. You don't need a merchant account, website of your own or anything else for that matter. All you need to do is be able to provide a high-quality service at a reasonable price. But be informed, you will have to compete with many others that are constantly bidding on open jobs.
Tutoring can be done in-home or online. The in-home tutoring will take networking and teaching experience to build your business. Online tutoring, however, can be done through companies that connect tutors with students while providing the needed infrastructure (i.e. web conferencing services) for a cut of the fees. Most require a college degree and teaching experience but for some those requirements may be negotiable.
Ratings. Whenever someone buys a book from you, they will have the opportunity to give the transaction a rating. This is when they’ll tell other potential buyers whether the book was in the condition that you described, whether it was mailed on time, and if your communications were pleasant and helpful. One bad rating can hamper sales, and a couple of them can downright stop them. Excel at customer service and your ratings will help your company grow.