Happened to me about 2 weeks ago, and must admit that I thought it completely unexceptionable, and handled exactly as it should be. GA called me before boarding and explained that they needed the seat; on boarding I saw the trainee sitting in 'my' seat and reading her manual; and as she made all the standard FA announcements it was VERY clear that she was new to the job and was on a steep learning curve. Can't see why this would be worth commenting about (although I guess that I just did).