Easy, give him the freedom to go after clients his way as it's worked for him in the past. As for the commission, base that on the amount of the sale with a scale so it's fair to you both. Commission only is rough, get to know your sales people personally. At times, a small base pay is good to keep their bills paid, gas in the car, travel etc.. as people need to eat and take care of family.
The base is purely for a limited time, like say 3 - 6 months as they are working for you. Don't micro manage, just each week have 1 on 1 meetings to know the progress and adjust since you do not want to repeat the same approach that's not working.
As the sales increase, start reducing the base then eventually remove the base as they are on their feet. It's also normal to provide advances to good salespeople and deduct from the pay in stages.
The main thing, be fair to you both.
I've experienced this for over 20 years as a salesmen, owner and investor in people. If you have specific questions or want to know more? I'm more than happy to advise, let's connect as I just joined and ready to assist you and others.