Animal contests are usually resolved when one opponent makes the decision to withdraw. This decision may be influenced by diverse sources of information available during a contest. Animals may reduce the costs of fighting by assessing the quality of their opponent and withdrawing when they determine that the opponent is superior (“mutual assessment”). However, as assessment itself may be costly or difficult, animals may adopt an alternative strategy of persisting until they reach a cost threshold (“self assessment”). We conducted a series of experiments to examine the sources of information that influence decision-making during male-male contests of the jumping spider Servaea incana. We considered both maximum level of escalation and duration as measures of contest costs and also examined assessment strategies used at different stages within a contest. There is substantial variation in body size in S. incana males and body size was a strong predictor of contest outcome. Despite the high acuity vision of jumping spiders and their dynamic, ritualized, displays, we found little evidence that S. incana males assess the size of their opponents during staged contests. Consistent with a self-assessment strategy, smaller spiders were less willing to escalate, regardless of opponent size. Contest duration did not vary in accord with predictions of either mutual or self-assessment and appears to be a poor metric of contest costs for this spider. Despite an apparent lack of mutual assessment during contests between live pairs, S. incana males did exhibit an ability to discern ‘opponent’ size in video presentations. We discuss both the limitations of correlative studies in studying assessment strategies and why spiders may not use information about an opponent during contests.