Questions to ask syndicators to prove they are not running a Ponzi scheme?

[Matt W.]

I've been diving into research about being an LP (limited partner) on many types of syndications, multifamily being the most common. As everyone knows, anybody who started a syndication in the last 5 years made money, so it's hard to tell good operators from bad. 

As J Scott has said in podcasts, if you're good enough at P&Ls and spreadsheets you can fool your investors. Many of the multifamily syndicators do so many deals, it would be easy to money from the latest deal to be going out the door to pay investors of the older deals, aka a Ponzi scheme. 

How can I specifically protect myself from this danger? I know the operator is the most important part of the deal and you can google and full on background search them for shady dealings, but is there a particular line item that would be a red flag in their financials?

Thanks.