Hi,
First of all, must understand the market and pricing first. In order not to let your agent cheat you, best is be firmed at your selling price.
Usual practise is 2% commission for agent as they need to do marketing and alot of viewing appointment liasing for you.
Nowadays, agent are more than willing to co-broke as CEA had already spelled out that agent are not allowed to have dual commission from seller and buyer.
As for guidelines for choosing agent, it will depend on how comfortable you are with the agent. Most important is get them up to your house and do all the financial calculation for you so as to test whether they are proficient or not, and also don't get forced by the agent to sign exclusive with them. Test them and ask them for a valid reason and advantages why exclusive is needed. A good agent will tell you the advantage and disadvantage to have exclusive or not.