I'm an accomplished woodworker and I looked into this and found no advantage to going online. I assume you know that shutters are always custom for the opening and I would have the installer measure the openings. That way, if a mistake is made you are not liable.

If you have window jambs that raises the bar even further since the measurements are exceptionally critical and the install is very difficult. If you have drywall jambs then the shutter comes with a frame.

There are some online sources that try to reduce cost by offering kits you assemble and finish yourself but I can almost guarantee you it's more work than you can imagine and your quality will probably be low.