Not just having your friend with a mid arm do it as a favor.
I don't see the difference between hiring someone who does it as a business and having your friend with a mid-arm do it. I would say friends with mid-arms who quilt for free are few and far between. Maybe I don't have the right friends...
Someone who does it as a business -might- be a better quilter than someone who does it as a hobby (there are some really great hobbyists out there and some really crappy "business" quilters, and the other way around too). If you want to show a quilt you would definitely want to find someone with exceptional quilting ability.
For me, I can't afford to hire a long-armer, so my answer is never.