Assessing QoE in Emerging Markets

For those of you searching or operating in emerging markets, I'm curious how you approach diligence with a significant "informal" or cash-based component to their revenue. While common in many regions, it presents a major hurdle for a formal QoE process and can be a tough sell to foreign LPs who are used to fully documented financials. What practical steps, verification methods, or frameworks have you used to get comfortable with the real numbers and successfully bridge that gap with your investors?