Hi.

If you purchase it from Odoo apps, There is no refunding scheme. But you can contact the author of module and then you can report your issues to them. They are responsible for you to provide service.

Also check this free module to hide the product cost price :  https://www.odoo.com/apps/modules/11.0/hide_cost_price/

See the attached image from Odoo apps FAQ

Thanks

1. Do test modules on a test server first.

2. You install non-Odoo modules on your own risk.

3. Modules may be in conflict with other modules you have installed.

4. Read the log entries to find and maybe repair the cause.

Hello guys. I'm the developer of this module. I just found this question. There was an email on bottom of the description pages of all modules. If you have any problems contact me via almas@dusal.net. No any other emails.

Regards

Hai, I purchased the same module from the same authors. What I notice when I add the folder of the module, the backend got blank page. But when I remove all the dusal modules, it works. Im using Odoo 11

I contacted the support@dusal.net but the developer is not reponding to my enquiry. 

you can try uninstalling the module directly in database

update ir_module_module set state='uninstalled' where name = 'your_technical_module_name'