a 10-day contract is better, since it's real work, for pay, but the relatively short duration doesn't tell you much about the candidate's intrinsic motivation or how relationships develop past the honeymoon stage.
so really, it'd be best and easiest if we all explicitly assumed that jobs had 6-12 month trial periods, for both parties, and that after that time, either can walk away without hard feelings (or negative judgment), other than in the most egregious cases (i've seen a couple cases that'd fall in this category). again, this is primarily about jobs that have the most variability. less variable jobs don't need as long of an evaluation period (but do need more than a few weeks).