How to track conversion of a free service to sale - ideas and experience welcome!

How to track conversion of a free service to sale - ideas and experience welcome!

Hello, we have a small selection of devices that we give to customers to trial before purchase. Once the trial is finished, they return the device and hopefully they proceed to purchase the device. 

We need a process within the CRM to better track conversion from trial to sale. Ideally we would also be able to automate the process further by creating tasks for the sales team based of the status of the trial device.  

We have heard some companies do this by raising an order for the trial  - so a quote is raised with a 0 value, an order raised and then returned/updated to a sale depending on the outcome. I'm not sure this is the way forward as we wouldn't have the automation of raising specific tasks.

How would you manage this in Zoho CRM? 

Thanks