Gotta love those runners! They're usually my first elders. Another way to quickly get a farmer to trainee is to set her on the coconut tree repeatedly, then when she starts to climb, whip her off & make her start again. It usually takes me betw 4 to 7 or 8 times (where she does climb) to get the trainee status.
Also, sometimes you'll get a villager who just plain doesn't want to work.