Theres heaps of fake files around at the moment, so try to select a smaller amount of hosts to download from...
But the best way to know if you have selected a geniune file is to use Bitzi, this thread will explain what it is and how to use it...
http://www.gnutellaforums.com/open-discussion-topics/37676-how-use-bitzi-web-lookup-how-use-magnet-links-direct-connect-browse-chat.html