There is no foolproof way, each individual develops their own workflow to install content.  The majority will unzip the files into a temporary folder to check the integrity of the runtimes then move them to their final destination, wherever that will be.  Others use a reliable installer of some type.  For me, I use DIM to install DAZ products, it is reliable and I am familiar with it.  For freebies, I open them in Winrar, examine them and then install the content into the appropriate runtime of my choice.  Renderosity has changed the way of installing content so that is not too much of a concern for me presently.