1. Start with what you can see
Note where drafts, fogging, or sash trouble show up, how long it's been happening, and whether it tracks with Michigan's freeze-thaw swings.
2. Look at the house, not just the window
Old West Side clapboard, newer subdivision vinyl siding, glacial-till drainage, and sun exposure all change what a proper installation requires.
3. Get it in writing
A real scope covers trim repair, flashing, disposal, permits if triggered, cleanup, and what happens if something's rotted behind the casing.
4. Line up more than one bid
Check that each provider is actually licensed to work in Washtenaw County, then compare how they'd handle the same hidden problems.
5. Don't sign off too fast at the end
Confirm the finish work, the warranty paperwork, and who's responsible for anything that shows up after the first winter.