A quote is a promise from a contractor to do the work at a fixed price. It's important to get it in writing and not to rely on a verbal quote. After you say yes to a quote, it’s a binding agreement between you and the contractor, whether it’s written down or not. But having it in writing means you can check what you agreed and prove it if there’s a dispute later.

The contractor can’t charge you more than the price on their quote unless you ask for extra work that’s not included in the quote, they let you know they have to do extra work and you agree to pay more for it or they made a genuine mistake when writing down or calculating the price - in which case, they have the legal right to charge you what it should have been.