  The subjective Bayesian interpretation of probability asserts that the rules
of the probability calculus follow from the normative principle of Dutch-book
coherence: A decision-making agent should not assign probabilities such that a
series of monetary transactions based on those probabilities would lead them to
expect a sure loss. Similarly, the subjective Bayesian interpretation of
quantum mechanics (QBism) asserts that the Born rule is a normative rule in
analogy to Dutch-book coherence, but with the addition of one or more
empirically based assumptions -- i.e., the "only a little more" that connects
quantum theory to the particular characteristics of the physical world. Here we
make this link explicit for a conjectured representation of the Born rule which
holds true if symmetric informationally complete POVMs (or SICs) exist for
every finite dimensional Hilbert space. We prove that an agent who thinks they
are gambling on the outcomes of measurements on a sufficiently quantum-like
system, but refuses to use this form of the Born rule when placing their bets
is vulnerable to a Dutch book. The key property for being sufficiently
quantum-like is that the system admits a symmetric reference measurement, but
that this measurement is not sampling any hidden variables.
