With the increasing popularity of nonprofit thrift shopping, new marketing strategies are needed to respond to accelerated competition in the secondhand market. To help guide the development of marketing strategies for nonprofit thrift stores, this study aims to identify factors impacting consumers’ buying behavior for secondhand fashion items sold in nonprofit thrift stores. Specifically, this study investigated 1) the effects of secondhand fashion selection criteria (i.e., design, brand name, lower price) and personal factors (i.e., gender, household income, beliefs about environment) on the secondhand fashion consumption experience in nonprofit thrift stores and 2) the moderating effects of point of purchase (POP) messages (i.e., “50% Off Sale,” “New Arrivals,” “Helping Others”) on the relationships between purchase intention and impulsive buying in nonprofit thrift stores. An online survey was used to collect the data, and a total of 197 usable responses were received. The results showed that 1) gender, household income, beliefs about environment, and brand name affected the secondhand fashion consumption experience and 2) the POP message “Helping Others” negatively moderated the relationship between purchase intention and impulsive buying in nonprofit thrift stores. These results can help nonprofit thrift stores’ managers to develop effective marketing strategies to increase their profits, which can be used to accomplish their mission of addressing social issues.