Yes, you can try many of our apps for free. All of our apps (excluding Product Discount) generally offer a 30-day free trial and can be installed through the Shopify App Store. When you install the app it will ask you to accept the charge, but if you look closely you'll notice the trial end date is 30 days away.
What about Product Discount?
Product Discount is a one-time charge app. Pay for it once, and it's yours for the life of your store. As a one-time charge, it can't be set up for a free trial.
What we recommend is that you install Product Discount, and accept the $99.99 app charge. If for any reason within 30 days you feel that the app does not suit your needs, remove the app and Email our Support Wizards to arrange a full refund.