Some other questions to consider asking:
How long have you been longarming? On the machine you use now?
Is your machine hand guided or computer guided?
Have you quilted for competition?
Are you a member of any guilds or machine quilters' organizations?
If I select a quilting pattern that you don’t think will look very good when complete, will you explain why and make other suggestions?
Are there brands of batting that you prefer to work with?
Will I receive an estimate?
Do you require a deposit?
Do you give a discount to first time customers?
If extra work is required, do you call in advance of doing that work?
Do you baste all the edges?
Do you trim the backing and the batting?
Do you also make quilts?
Do you have any problem with cats? (some here will not take customers with cats because of allergies)
What type of thread do you use? Do you supply it?
Do you have a rush service?
Are there any size limitations, large or small?
Do you require backstitched seams on the edges or is perimeter stitching okay instead?