I really like nlgutter's website. Excellent example of video use to help in the branding; if advertising draws people to the site, they are largely sold by the time they call you for estimates.
So the question you are asking is what kind of closing rate should you expect. High (I'd say with some qualification, from 60 to 70 per cent), if from the leads you provide; lower if they are going out and finding their own work. There is an argument for differential compensation -- lower commission when leads supplied than if they canvass or otherwise find the clients themselves. This is fair, of course, because they will either/or have a lower closing rate or they are great salespeple. You might expect your reps to find a certain percentage of their own work as part of their compensation.
There is also an argument (heresay to some!) that your reps working leads provided by you should earn a salary rather than commission (but hire using stringent evaluation processes to ensure they are competent as sales reps).
The latter stringency in hiring is also your insurance whether you hire salaried or commission reps that you will get the right person. Expect to search harder, with more pain and frustration, and lower results if you are going the pure commission route, but don't deviate from your standards just because they are 'on commission'. As you've noted, you can't afford bozos burning your leads-- or your brand.