This script has only been tested under Greasemonkey 4 (Firefox), ViolentMonkey (Firefox), and TamperMonkey (Chrome) but should work on any other UserScript host which provides the necessary GM_* or GM.* APIs.
The settings dialog is accessible via a "Configure Sale Helper..." option which appears either in the page context menu (Greasemonkey 4) or the userscript menu (all other userscript hosts) on relevant pages.
Currently, after editing the settings, you must reload the page to apply changes.
If you don't collapse GOG's filter groups in the sidebar, you're likely to be left with a big gap between the non-hidden games and the paginator.