  Meson mixing is considered to be an ideal candidate for new physics searches.
Current experimental precision has greatly increased over the recent years,
excelling in several cases the theoretical precision. A possible limit in the
theoretical accuracy could be a hypothetical breakdown of quark-hadron duality.
We propose a simple model for duality violations and give stringent bounds on
such effects for mixing observables, indicating regions, where future
measurements of $\Delta \Gamma_d$, $a_{sl}^d$ and $a_{sl}^s$ would be clear
signals of new physics. Finally, we turn our attention to the charm sector, and
reveal that already a modest duality violation of about $20 \%$ could explain
the huge difference between HQE predictions for D-mixing and experimental data.
