The questions that separate the quotes

"What is your licence number, and who holds it?"

Then look it up. You are checking that the licence is current and that the name on it matches the name on the contract you are being asked to sign.

"Can I see a job you finished five years ago?"

Anybody can show you a roof completed last month. A roof that has been through five winters shows how the edges, valleys and penetrations were actually detailed.

"What happens if the decking is rotten?"

The right answer is a specific price per sheet, written into the contract before work starts. A vague answer here is how a fixed price stops being fixed on day two.

"What does your workmanship warranty cover, and for how long?"

Ask for it in writing, in the company name, with a term. Five to ten years is common; the term matters less than whether they will still be trading.

"What underlayment, and how are the valleys done?"

This is the question that reveals whether you are comparing the same roof. Underlayment, ice-and-water placement, drip edge and valley treatment are where quotes quietly diverge.

"Who is actually doing the work?"

Ask how long this specific crew has worked together. Roofing companies keep their name and change their hands more often than most trades.

In short

Six questions, three contractors, one afternoon. It is the cheapest insurance available on a job this size.