In order to distinguish individual contributions of trihalide anions in beta-like structures of the (BEDT-TTF)(2)X organic conducting single crystals [where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X stands for I-3, I-I-Br, Br-I-Br, Br-I-Cl, Cl-I-Cl or mixed trihalide anions], low frequency Raman spectra have been recorded at 25 K. This technique permitted us to establish a presence of a ternary mixture of I-3, I-I-Br, and Br-I-Br anions in one of the nonstoichiometric salts and an existence of Br-I-Br, Br-I-Cl, and Cl-I-Cl anions in another one. It is not possible to detect these anions independently using the x-ray diffraction method. The ab initio calculated interatomic bond lengths and vibrational frequencies of trihalide anions are in good agreement with experimental data, which confirmed the assignment of observed low-frequency Raman bands. At 80 K the Raman spectra were taken for a fixed linear polarization of the incident laser light, and the examined single crystals were rotated in pi/8 increments. In this way, an anisotropy of trihalide anion's polarizability has been investigated to confirm the collinear arrangement of anions and the proposed assignment of Raman bands.