Online educational marketplaces have seen remarkable growth, but have had little empirical investigation of the quality of materials, particularly in social studies. This exploratory study examined characteristics and quality of secondary U.S. history resources on TeachersPayTeachers.com. Findings show that activities were esthetically well-designed, but 70% were of "moderate" or "low" overall quality according to our rubric that assessed areas such as higher order thinking, connections to student experiences, and representations of multiple perspectives. Thirty percent of the activities were found to be potentially harmful to students. We discuss implications for teachers and online marketplace accountability.