How to evaluate amps that are not broken in?

Doesn't it seem odd that "break in" always seems to result in an improvement, never a change for the worse?

My experience with human nature is that those with a passionately held and generally negative position will press their case vociferously and indefinitely, even in the face of volumes of contradictory evidence, particularly if this evidence does not square directly with their own experience, perceptions, or sense of fairness. - Knownothing

Depends on what one considers and accepts as evidence. Loads of anecdotal evidence is nothing more than loads of anecdotal evidence.