You're going to wind up trading a fixed rate for a variable rate (equity lines come with variable rates) on the money. 

They should be able to pull some comps that will give you an idea of what rehabbed properties are trading for in your area.Hope this helps! 

The reality is that this is a strong seller's market and a lot of inventory is trading whether or not the numbers make sense.

In the future, we plan to build a secondary exchange on which these investents can trade such that investors can sell their stake before the property is sold.  

Me personally I look for value add deals that are already performing that will allow me to increase the valuation so the property will trade at a higher multiple on the exit.

If they provide wrong or incomplete information and you base your offer on that information, then you'll have grounds to re-trade the purchase price during the contract period.

There are some significant trade-offs to exit the investments.

If the real estate entity is engaging in a trade or business such as new property development for immediate sale, or flipping of properties, that can generate exposure to taxation on UBTI, which can be more detrimental to the ROI. 

That's the trade-off.

Otherwise your other option is to get various trades to sign off on their respective components (Plumbing, Electrical, HVAC, Structure, etc.).