Citadels first game setup for 3 players
I've read the Dutch rulebooks of the base game and the expansion. The expansion introduces the ninth character, and it states that in a 3-player game, you only have 8 characters. It's highly recommended to leave out both the Tax Collector and the Artist.

Note that, as mentioned in the comments, the original game had only 8 characters. The expansion came with 10 characters in total: replacements for characters 1-8 and two picks for spot 9. So now, you can pick from two characters for each spot in the turn order. However, as mentioned in the rules (here - and in Dutch -, for completeness sake) 3-player games (and by extension, 2-player games) should e played with only 8 characters.