Unless you have a long standing relationship with this person, I would definitely not structure it like a "partnership" with equal splitting of everything. Instead, consider drawing up the whole scenario with how you think it will go and then one of you becomes the developer and the other becomes a lender. Meaning...
Let's say it's $100,000 to purchase and $25,000 to rehab, selling for $185,000. If this were an all cash scenario, you each bring $62,500 to the deal, but one of you is the lead developer and title holder, and the other puts a lien on the property. Each of you gets a guaranteed pref on the $62,500 you each put in, and then you split profits 50/50. That way only one of you is making all the developer decisions so there will never be a fight. Whoever becomes the developer should also be prepared to bring more money to the table to complete the job if the costs balloon (rehab, holding costs if you are a getting hard money in first position, etc). But keep in mind that bringing that extra money also comes with the pref, so it is not for nothing. You can also have an agreement that the realtor in the equation will take a discounted listing fee, but they are at least making something as well no matter what it sells for. The point I am trying to make is that you can get creative and slice up the profit sharing any number of ways -- just as long as you don't do it as equal partners expecting to make equal decisions and still come out of this as friends.