While numerical bipolar rating scales may evoke positivity bias, little is known about the corresponding bias in verbal bipolar rating scales. The choice of verbalization of the middle category may lead to response bias, particularly if it is not in line with the scale polarity. Unipolar and bipolar seven-category rating scales in which the verbalizations of the middle categories matched or did not match the implemented polarity were investigated in randomized experiments using a non-probabilistic online access panel in Germany. Bipolar rating scales exhibited higher positivity bias and acquiescence than unipolar rating scales. Reliability, validity, and equidistance tended to be violated if the verbalizations of the middle category did not match scale polarity. The results provide a rationale for rating scale verbalization.