Victor,
Welcome! I'm in Gwinnett county as well.
Most of the advice here is "on point." I think the 50/50 split is a good start. Keep in mind that if the home is listed, then a Realtor would make 2 to 3% and if he sells the home then a good question is he going to charge you a commission? To me (also a realtor/investor) the commission is in the deal on a 50/50 deal. That means when we retail it out I'm not taking a commission, I'm splitting the profits. On the buy side I may get a commission but that goes into "the pot."
In terms of evaluating a deal, I really hate "BP" posts that suggest there is a formula. If you're only making 10% on a deal but the deal itself is lower risk or have other intangibles that you might want then it's not a bad deal. What I do agree with is setting up minimums so you have boundaries. It could be 20K profit and 10% Gross ROI or 20% etc.
In Gwinnett and more desirable areas the margins are smaller but so is the overall rehab challenge, it's also easier to retail the property vs Atlanta where you might have more rehab challenge, etc. Risk vs Reward. Would take 10% all day long if the deal is easy.