I believe the sequence of presentation during a seminar or product presentation will tell you what they have placed importance or take precedence in their prospecting.
If they start by showing you all of their achievements, and talks little about their product, you can be sure where this is going to lead. And if anyone of them says it will be easy to sell, from their mouths but you still have doubts about the product's value and ability to sell, do not continue to join. You can be sure you ain't able to market something you ain't confident with or will use yourself in future. And thus, you will fail.
MLM that put emphasis and focus on product selling, it is as sustainable as any other wholesalers or retailers. MLM that focuses on recruitment, will have difficulty sustaining in the long run.