Can I customize app features?
It depends on app features and your plan. For basic plans backend source code is not provided and you will receive it in precompiled form but you can still customize clients and dashboard.
Can I run this app in my country?
The important thing to consider would be localization. On language level it’s very easy to translate words and currencies to your own locale with translation files being separated from code. You also might need to check Braintree, Stripe & PayPal Websites as provided to make sure they are supported in your country.
What is your refund policy?
If customer finds a bug and fix wasn’t provided in 15 days after report it would be eligible for a refund.