In the epic game, Commercial doensn't give you any cheap buildings. I don't understand the "pays for trade instillations" part. Smith's Trading Company pays for all trade installiations. Smith's goes with the Commercial trait. No one gets any discount on any small or great wonders. The editor might have an error somewhere. I know in a recent 20k Sid attempt, which turned diplomatic, where I played as Korea. I built the Forbidden Palace and the Great Library (scientific trait satisfied here), but I did NOT get a golden age when I had both of these in. I did, however, get a golden age when I finished Smith's. My guess is either Calis had it right, or the editor simply has an error.