Just an idea: May be you can offer a chargeable service to look at the source code of 3rd party plugins and check if they have security leaks or something else. If they are ok they get a certificate (just an award/image etc.) so users can see that this plugin should work fine and do not make problems. May be the author of the plugin wants to sell it and could get an advantage by using this service.
Nobody can work for no money and the pro version of the admin plugin is one way to get back a liite from all your effort. May be such a service would help too.