You're right, stretching canvases properly is a skill. A hard one to develop when you are already involved with so many other tasks. And I find even more difficult to get staff to wrap their heads around.
If you are looking for true high-end product I would partner with a respected high-end framer. You client is going to want keyed mitres and keyed spars. What weight canvas are you using, is it archival and what coating will be applied? Getting into the game at this level could be a real rabbit-hole.
Maybe even let the framer have the job and create a partnership for you other services.