Yeahhh... Square does a bad job hiding villains. Seymour, Kuja, Dysley, Vayne, Edea, Golbez...
Seymour and Vayne are the only ones out of this that you weren't supposed to immediately identify as evil. When I first saw Golbez there was some doubt in my mind though.

They did throw me for a little but of a loop with Seymour, as soon as I saw him I immediately thought "Final Boss!". Kind of weak considering you weren't supposed to know he was evil at all.

When I first saw Vayne I judged him as a fair and just ruler who would probably do a better job of ruling Dalmasca that the hereditary appointed monarchy that the empire displaced. It was also obvious that they couldn't let someone in his position be benevolent, and he would be a major villain of the game.