Ask whether the gutters will be formed at your house, and what metal and thickness they’ll use. Aluminum is the most popular gutter metal, and a This Old House guide favors .032-inch aluminum over the lighter .025-inch because it’s sturdier.
Ask how the corners and outlets will be joined and sealed, since those are the seams that remain. Ask what size gutter and downspout they plan. Five-inch gutters are the usual size, and 6-inch gutters paired with 3-by-4-inch downspouts carry more water off a large or steep roof.
Ask what hangers they use. Hidden hangers screwed into the fascia hold up better than the older spike-and-ferrule kind, which can pull loose over the years.
Get the quote in writing with the length of each run, the gutter size, the metal thickness and the number of downspouts, and ask for proof of liability insurance. SirGutters lists companies based on what their own websites say and doesn’t check a license or an insurance policy.