I’ll plus one all of this to say that I regularly do this, as do my collaborators. I’ll add that it not only doesn’t hurt to ask, and (as long as you’re asking it in the professional way they all suggest above) it’s an indicator that you care about learning and continuous improvement, traits that could boost your reputation in the potential clients’ eyes. In your note you can make that clear by emphasizing that “in the spirit of learning and continuous improvement…” etc.