I have purchased a house which I plan on flipping.We have bought $5000 worth of windows and they are currently being installed by our contractor. I noticed today that he is framing these windows with plywood.
Seems to me that this method would not last. Is this an acceptable way to frame new windows?
Thank you for your assistance.

Where and how is he using the plywood? Pictures?

He is using the plywood on the exterior. The interior portion of the windows is framed with studs. There will be siding that covers the exterior plywood.

That is perfectly acceptable and standard practice, without it your jamb depth into the wall would not be correct. I would, however, further seal the plywood and studs with at least some tar paper prior to applying the siding.

What you describe is a common method to fill in around a window. Instead of tar paper, I would ask the contractor to use tyvek housewrap.