IFS questions

I have been playing AE off and on since 2006 but I haven't worked much with the IFS system.  I have read a few posts on it but I'm not entirely sure what is going on yet.  Can someone help me figure out what the best balance between profit and rating is?  And what exactly is the scam IFS that everyone speaks of and why is it bad?  How can you tell what type of IFS the other guy is running?  Thanks for any help!  I appreciate it!

Andrew