I have done that a few times with younger applicants (their first or second apt's usually)  who had enough income,  but didn't have much or any credit history or prior address history and in a couple of those cases it became very valuable that there was a co-signer involved.    

I think there are ways to create a moat or put a fence around your clients by creating and using valuable-to-the-end-user proprietary intellectual property.

Hey @Steele Evans, It depends.

I have framed up a question specific to my experience, but have also posed a very general question that may be more valuable to answer.

That is valuable information to screen and make informed decisions without putting any of my own effort into that specific person. 

Looking at what you could possibly get for the price per sq.ft is valuable.

As Scott mentioned, it is vitally important to run your own numbers -- what the seller tells you sometimes qualifies for a Pulitzer Prize in Fiction.I forget how many times BP lets you use the calculator before you have to become a "Pro" member, but even the first time is a valuable education.

They are extremely valuable to you. 

Your hustle is likely more valuable at this stage than your current available capital, especially in an expensive market like So-Cal.

At this point, and in order to have an amicable outcome, I would go with a 50/50 split plus your 20k, and call it a day and a valuable learning experience.