  Merging beliefs requires the plausibility of the sources of the information
to be merged. They are typically assumed equally reliable in lack of hints
indicating otherwise; yet, a recent line of research spun from the idea of
deriving this information from the revision process itself. In particular, the
history of previous revisions and previous merging examples provide information
for performing subsequent mergings.
  Yet, no examples or previous revisions may be available. In spite of the
apparent lack of information, something can still be inferred by a
try-and-check approach: a relative reliability ordering is assumed, the merging
process is performed based on it, and the result is compared with the original
information. The outcome of this check may be incoherent with the initial
assumption, like when a completely reliable source is rejected some of the
information it provided. In such cases, the reliability ordering assumed in the
first place can be excluded from consideration. The first theorem of this
article proves that such a scenario is indeed possible. Other results are
obtained under various definition of reliability and merging.
