Make the site conditions visible
Photograph the inside and outside, measure the opening, note the height and access route, and list the cladding, trim, stool, roof or seat detail, and nearby utilities. Ask the installer to state which conditions were observed and which were assumed.
Separate the unit, demolition, opening, support, flashing, exterior finish, interior finish, access, protection, disposal, and allowance lines. If the estimate uses a contingency, tie it to a specific inspection finding instead of accepting an unbounded percentage.
Limits
No property was inspected and no price is supplied. The U.S. Department of Energy guidance supports a whole-window and installation view, not a quote for a particular home.
Sources and related reading
See Also
If you want to move from general advice into actual product choices, start with Are Bay Windows Worth It? A Maintenance and Fit Decision, Bow Window Replacement Quotes: What the Estimate Should Separate, and Circular Saw Buying Guide for First-Time Buyers in the U.S.: What to Check.
For a wider picture after the basics, Smoke Alarm vs. Carbon Monoxide Detector: Which One Better Protects Your Home? and Klein Tools ET310 Review: A No-Nonsense Circuit Breaker Finder are the next places to read.