That way you know the funds are ready and investable. 

A HELOC or cash-out refinance would let you access funds for the down payment on a new property without needing to sell or relocate.

Any remaining funds after paying the mortgage can be kept by the property owner. 

It's like a mutual fund vs owning one stock!

If you are planning a hands-on project or know someone else willing to work side by side with me, I am ready to provide funding for the right deal.

Opportunity Zones are designated distressed areas where long-term investment and development are encouraged.3 Reasons Why You Should Invest in Opportunity ZonesDefer or Eliminate Capital Gains Tax ObligationsWhen investing in Opportunity Zones through a Qualified Opportunity Fund (QOF), you have the potential to defer your capital gains taxes.

Asking for proof of funds is reasonable.

If you are retirement age, you can do asset based withdraws from "work related funds" (IRAs/401ks...).

Lastly, don't forget to get estoppels when you close, that is the tenant signing off on the current rental amount / funds you have escrowed. 

I made the decision to purchase a 6 unit building with those funds that will eventually cash flow $4200/month.