The purpose of this paper is to investigate the e-commerce credibility factors affecting the perception of users in Saudi Arabia and, moreover, to investigate whether the variation of credibility factors in Saudi Arabian e-commerce websites influence users' performance. Website credibility, which refers to the believability of the website and its content, plays an important role in consumers' successful online shopping experience and satisfaction. This investigation is conducted by employing two credibility evaluation methods: heuristic evaluation and performance measurement. This study adopts Fogg's 10 Stanford credibility guidelines as a starting point for the heuristic evaluation. In the performance measurement method, two measurements are used: the amount of time needed to finish the task and the total number of clicks taken to finish the task. A frequency analysis of the comments and a one-way ANOVA test are used to establish the results. Three e-commerce websites in Saudi Arabia are selected. The findings show that Fogg's 10 Stanford credibility guidelines can be implemented in the Saudi Arabian e-commerce context with minor modifications and expansions by adding reputation, endorsement, security, and service diversity guidelines. Another important finding is that professional website design plays a vital role in users' first impression of websites, while usability is the most important credibility factor investigated used to evaluate the credulity of an e-commerce website. Lastly, the results of this study indicate a relationship between the e-commerce credibility level and users' performance. This paper contributes to the literature by providing a set of credibility guidelines associated with specific criteria, which can be assessed to improve the future of e-commerce in Saudi Arabia.