we find it difficult, too, to find good perl developers in our area (berlin, germany). many overestimate their abilities, or they aren't team players.
i personally like small programming tests. of course the test must fit to the candidate's experience.
i wouldn't say one has to know A, B and C to get hired. it depends on what one did before. a perl starter who doesn't know references might learn them quickly.
an expert in OOP who doesn't know how to debug efficiently might not be the best candidate.
also a trainig day might be a good idea.