Four items assess a consumer's perception of the justness and equitability of a specific sale price for a product.
Hardesty, D. M., Carlson, J. P., & Bearden, W. O. (2002). Brand familiarity and invoice price effects on consumer evaluations: The moderating role of skepticism toward advertising. Journal of Advertising, 31(2), 1–15.
Free access to 2023+ psychometric scales at PsychScales