Prejudice, Bias, and Stereotyping -ever justified?

Bassham (p, 16) writes that the peculiar characteristic of prejudice and stereotypes is to be based on "unwarranted assumptions," and that they should hence be rejected.

This probably earns an immediate "of course" from roughly everyone today, which makes it puzzling how someone like Edmund Burke could have written: "Prejudice . . . is of ready application in the emergency; it previously engages the mind in a steady course of wisdom and virtue, and does not leave the man hesitating in the moment of decision, skeptical, puzzled, and unresolved. Prejudice renders a man's virtue his habit."

One view is that both 'prejudice' and 'stereotype' are relative terms - relative to both the particular nature of the grounds/evidence upon which they are based and to the sorts of concrete frameworks in which they function.

Let's say I have a prejudice that leads me to prefer not to deal with Finnish used car dealers. (a) This might be based psychologically on, e.g., an uncomfortable feeling about blonds (I trust everyone notes the prejudices built into this!) (b) On the other hand, it might derive from my having been being thoroughly bamboozled by a Finnish used car salesman last year, in which case I have one piece of evidence somehow relevant to grounding my prejudice. (c) Or I might have, say, 23 cases from among my family and friends where this has happened, spread over several years and several locations. Here, I have a different order of evidence, which might provide the basis for an empirical generalization (which may itself be more or less adequate, depending.) (d) Further, I might have other types of experiences with or knowledge of Finnish culture which lead me to think that it contains social mores supporting a tendency to be less than 100% honest in commercial dealings; this would provide quite another sort of ground.

Now I wander into Frithoj's used car lot, notice the owner is Finnish, and decide: "I'm outta here!"

(1) I don't know Frithjof; I have no information about him except his nationality. I am acting on the basis of a prejudice/bias/stereotype. But is the (degree/sort of) irrationality exactly the same in cases (a), (b), (c) and (d) above? What happens when, at some point, a prejudice comes to by supported by (various kinds of) evidence. (We might label this a "postjudice".)

My question to you: what sorts of things might "justify" a prejudice, or justifying acting on prejudice (if that is possible at all), and what sorts of evidence might be relevant here?

I don't know Frithjof. He's an individual, not a group or a culture. Thus, as Bassham points out, drawing or acting on any conclusion about him on any of the above grounds is (in this respect) unjustified (and perhaps immoral as well)! So, assuming that I do have "grounds" for a prejudice: in which sorts of cases can I reasonably/morally make decisions on the basis of it, and in which not? And why? Does it matter, for example, whether the case in question is one where Frithjof's wellbeing - or mine - is affected in some major way?