The charge-fluctuating and charge-ordered states in metallic, insulating and superconducting bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) salts are characterized through the analysis of the infrared (IR) spectral region relevant to the C=C antisymmetric stretch, b₁ν₂₂. This spectral region shows dramatic changes in band intensity and band-shape by varying the temperature. The observed spectral features can be understood on the basis of an extension of the well-known Kubo model for the spectral signatures of an equilibrium between two states. The two-orders of magnitude increase in the IR oscillator strength of the b₁ν₂₂ mode upon ionization has also to be taken into account. BEDT-TTF C=C antisymmetric stretch, b₁ν₂₂.