Ethics remains a critical area of negotiation research, yet existing measurement tools in this field have unexamined limitations. This study critically analyzes the Self-reported Inappropriate Negotiation Strategies (SINS II) scale, as the most prominent instrument for assessing Ethical Ambiguous Negotiation Tactics (EANT). By examining 12,375 data points from 495 respondents, the research reveals significant challenges in the scale's application. While confirming the scale's statistical reliability, the study uncovers key methodological concerns, including content validity issues, potential social desirability bias, and the need to account for participants’ missing familiarity with specific tactics. The analysis explores how socio-demographic factors influence negotiation ethics, with notable findings on cultural differences, age effects, and the complex relationship between negotiation experience and ethical behavior. The research provides crucial insights for future negotiation ethics studies, highlighting the importance of nuanced, contextually sensitive approaches to measuring ethical decision-making in negotiations. These findings offer valuable implications for negotiation training, cross-cultural research, and understanding the subtle dynamics of ethical behavior in business interactions.