How should I structure this deal?? Suggestions welcome

[Adam Karrera]

Hello BP forum members!
Wanted to reach out and see if anyone had any suggestions on the following scenario.

Friend of a friend has a condo in Phoenix. Her 20-ish year old son made a mess out of it with cigarette marks,

holes punched in the drywall, scuffs on the walls, carpet stains, etc.  Its all superficial damage, from what  I can tell,
but of course I'll get a professional inspection before doing anything.

Anyways, the condo is empty now, and her son moved out of state.

She has made the payments, but never fixed anything inside.

I asked if she was interested in selling and she said definitely is.

She is asking for about 70% of market value, but I want to offer her 50% now + an 

equity split after I fix / resell it.  She is underestimating the repairs,... but in either

case, she doesn't have the $$$ to fix it up herself.

So, how do I create a win-win situation for a family friend, but still protect myself from

her or her son changing their mind?  I don't want to fix it until its in my name, for obvious reasons.

How do I promise a % of the net?  I was thinking a promissory note, but I don't know if you can do % of equity using one.

I will check with a RE attorney before we sign anything, but just curious what suggestions

you guys/gals have on structuring some kind of deal like this one?

Thanks in advance!