Android: PRO version of the application. How to do it better?

Question

Android

I decided to make an upgrade to the PRO version with extended functionality in my application. The question is how best to do it.
It is not possible to use your own server to check payments, so now I did this:
After buying an item, I do not consume it. Periodically, at startup, I try to get a list of items, and if it contains an item with a PRO version, turn on PRO, if not, turn it off.
Worried about how the return of goods will work in this case. As far as I understand, if I did not consume it, the user can return this product at any time?
If so, is it even possible to sell the PRO version without using a server? And it turns out, users let me hold their money while they use the extended version.
I will add. The sale must be carried out on a Google account, recording the purchase in preferences before consumption is not suitable.

Answer 1

The "Pro" tovvr must be "non-renewable", i.e. its type must be "controlled by google". Read about what types of goods are available.
To do without a server, you can really just request the purchases that the user made at the start of the application, and if he bought the pro version and did not cancel it, save the necessary information in Preferences.