Henry's Eavestroughing

in 2006 requested a quote for eavestroughing on our new building. We agreed to the price and materials on the day of installation. The owner remarked that we needed to upgrade from 4" to 6". We asked how much that would cost in addition to what was already quoted. He responded about 20% more. The work was fine. But when the invoice came it was triple what had been verbally agreed upon.