Gazebos vary dramatically in size, roof weight, hardware, and assembly time. A 10×12 soft-top model is a different project from a 12×20 cedar pavilion. That is why the quote starts with the exact product link.
Send clear photos of the installation area and confirm what the structure will sit on. The site should be accessible, clear, and level before the crew arrives. If a new slab, footings, deck reinforcement, electrical work, or permits are needed, those items should be resolved separately before installation unless explicitly included in the written scope.