By default WHMCS do not have any kind of restriction on user registration that is without email verification a customer can able to perform all task. But using Email Verification Extended your customer won't be able to perform any task.
There is No Refund Policy applied on the module license whether it's onetime or yearly payment. If you are facing any issue on the module installation or so you can open a ticket with us or if you have any query or you are not sure about this module, you can email us or talk to us via our live chat. Also we would like to say that the modules are developed based on WHMCS latest version so we will not be supporting LTS version of WHMCS or any kind of nulled WHMCS.