Check the specification
Confirm the quote names the manufacturer, the exact product line, the frame material, the glass specification, and the colour and grille options — for every opening. ‘Vinyl casement, white’ is not a specification; the model and glass details are. If any opening says ‘TBD’, the quote is not finished.
Check the scope
Verify the count of windows and doors matches your brief, and that each is listed by room or opening. Confirm the installation method for each, who handles trim and capping inside and out, who disposes of the old units, and what happens — and at what cost — if rot is discovered. Verbal assurances about scope do not count; only the written document counts.
Check the terms
Read the payment schedule: a reasonable deposit with the balance on completion is standard; large upfront payments are a warning sign. Confirm the start date or start window, the expected duration, and what happens if the schedule slips. Check the warranty documents — both manufacturer and installer — are attached or referenced, not just mentioned.
Check the company
Confirm the business is who it claims to be: a real address or service area, a working phone number, and a written contract under the company’s legal name. Ask how long they have operated locally and what happens to your warranty if they close. Then sleep on it. A quote worth accepting is still worth accepting tomorrow.