No. An appeal to authority would be "this must be true because someone authoritative said it". Saying "I am willing to treat this claim more credibly than other claims because the source is credible" is not a logical fallacy.
That's a personal heuristic - a very reasonable one, but it's still an argument from authority.
A fallacy assumes a cogent argument is being made. This is just a preference.
Whether you say "it must be true", or "it is likely to be true" does not matter. Credibility must only come from the statement itself and the evidence to support it.
However, while it is a logical fallacy, it is reasonable to temporarily hold beliefs for or against the truthfulness of a statement while no or insufficient evidence is present. As long as belief is not mistaken for proof, nothing is wrong about having such gut-feeling.
I think you are confusing deductive and inductive reasoning.