How do I figure out NAV erosion in an ETF?

Say there's an ETF with great returns. How can I tell if it's just returning my capital to me, versus doing some good trading to get those returns? IOW, what if it's a Ponzi scheme? Are there any documents (like S-1s) filed with SEC that will help me answer this question? Thanks! submitted by /u/siskyouthrowaway [link] [comments]