  The insulating ternary oxide YbFe$_2$O$_4$ displays an unusual
frustration-driven incommensurate charge-ordering (CO) transition, linked to
possible ferroelectricity. Based on high-resolution synchrotron data, we report
a detailed structural model showing that the CO phase is an incommensurate
charge-density wave and cannot be ferroelectric, since the electrical dipole
moments are also incommensurately modulated. The change between continuous and
"spotty" helices of scattering at the CO transition is attributed to
three-dimensional fluctuations of the direction of the ordering wavevector.
