Do not forget to check for viruses before downloading. Or then only download from trusted sites. But mods are clearly worth it, as there is a whole new interest in games.
Mods are usually not distributed through the Google Play store. That is, they are posted on various sites. To run these files, you need to enable this action in the device settings.
This is done as follows: Settings - Security - Administration - Allow the installation of applications from unknown sources.
After that, you can download games with mods and install them directly. However, in some cases, you will need to uninstall the original application.
As for paid applications, I prefer to download Android games for free. As for the mods, I can say that they usually come with installation instructions. I saved a lot of money this way by downloading professional software.