if ya'll are talkin about the same thing like when the song you download turns out to be a loop, this is what i do when i use kazaa...
before you click to download a file, hover your mouse over the file and a little info window about that file will pop up. this window shows the size, album, artist, etc. you want to look for the "filename" in this window. if the filename is in all capitals or capitalizes whole words, then its probably the single or a loop file. i found that the real tracks usually have a 3-letter tag in the file name or just use all lower case (like wcr or rns). after you start paying attention to the file names you'll be able to avoid the fake files and be able to recognize the real ones easier...
hope that makes sense...