There are fake files throughout the network. Typically, these have heaps of sources (in the hundreds) but can also show up with lower numbers of sources.

If you're searching for music, try the All Types search. Search for album or artist rather than song title. Go for a file with 10 sources or less, or even a single modem source

When searching for movies, always check the file with Bitzi before download. If a file has heaps of sources but no Bitzi rating, chances are it's a fake.

Check out the threads below for more info, including how to use Bitzi.
Fake files showing up in search results
How to find music (tips for video as well)

Pro connects you to 5 ultrapeers, compared to basic's 3. So the potential's there for better search results (ultrapeers are people with fast connections who help with searches). But you probably won't see a big difference unless you're searching for rarer files.