Zoho Books for Service Enterproses

Zoho Books for Service Enterproses

I would like to know how to use Zoho Books for services such as car rental, travel agency, and hotel services. I notice that Zoho Books is good for goods, but for services, it's very difficult to track the profit or loss on each invoice. I need to capture the purchase price as well as the sale price when I process an invoice so I can track its profit, but I can't see how to do this.