You might find this interesting applying to your techniques: How to find music
Also check all way thru this thread .. tips on spam recognition, though I'm sure you know most of them by now: Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see) .. not only being related to size ... size counts though
Bitrate or should I say no bitrate is a major telling sign .. but there are some that are 'still' spam but are corrupted .. knowing how to tell bitrate v's file size makes a big difference also. Those types of spam (corrupted) were more-so spammed a couple of years ago .. less so now compared to others.