My question on avast is: How do we know it has completely uninstalled from our devices? Given the reputability of this company whose to say they don't leave som

My question on avast is: How do we know it has completely uninstalled from our devices? Given the reputability of this company whose to say they don't leave something behind after we uninstall. It would be great if someone with the means could do a before and after test to verify this.