To incentivize people to Volunteer for your Jobs, you can offer them a Discount to use on other Products. If they cancel, then they lose the Discount. If they have already made a purchase using that discount, then a balance due will be added to their account for the discounted amount.
Like any other type of Discount, first go to Settings->Discounts and click "Add New Discount". Give the Discount Name, Date, and Quantity values, choose how much it should be worth, and click to Save. Here, I am giving a 100% discount on the product price.
Click to Add a Requirement, and choose Discount Type called "Any to Any". This Type of Discount has the following options:
Here, I am allowing an Account to use the Discount once, and the Products don't have to be in the same order.
Go to Products, find the Volunteer Event that will act as the Source of the Discount, and navigate to the Assignments tab. Find the Any to Any Discount Source Assignment, and drag the Discount to the Assigned column, and ensure that it is set to "Apply".
Like any other type of Discount, Locate the Product that will be Discounted, navigate to the Assignments tab, and Assign that Discount.
If a Customer purchases the Discount's Source (the Volunteer Event), consumes the Discount, then Cancels, they lose the Discount. This results in a Balance Due on their Account.