Exactly! They purchase the service together with the product and once it is delivered and the job complete, payment is given to the service provider. 

During the checkout process, buyers select 3 preferred dates and time frames. Amazon gives the option to accept the job to relevant service providers based on their algorithm (area, time availability, service score..). The service providers will confirm the appointment arrival time frame over email, in most cases, or by phone. Payment is issued directly from the card the buyer has on file in your Amazon account.