We find that if we live at the center of an inhomogeneity with total density contrast | \delta _ { 0 } | \simeq 0.1 - 0.15 , dark energy is not a cosmological constant at 95 % confidence level .
Observational constraints on the equation of state of dark energy , w , depend strongly on the local matter density around the observer .
We model the local inhomogeneity with an exact spherically symmetric solution which features a pressureless matter component and a dark-energy fluid with constant equation of state and negligible sound speed , that reaches a homogeneous solution at finite radius .
We fit this model to observations of the local expansion rate , distant supernovae and the cosmic microwave background .
We conclude that the possible uncertainty from large-scale structure has to be taken into account if one wants to progress towards not just precision but also accurate cosmology .