: This paper is motivated by the dilemma faced by firms who sell new and remanufactured products offline that need to consider whether to enter e-commerce platforms considering that more and more consumers are shopping online on e-commerce platforms rather than shopping offline. Our paper aims to help firms with new and remanufactured products make a channel choice and determine product pricing strategies in the contexts of e-commerce and carbon tax policy. Our paper uses optimization theory, game theory, utility functions and profit-maximization models to investigate the optimal channel choice of whether a firm should enter an e-commerce platform; it also investigates the optimal prices of new and remanufactured products and referral fees in two cases—the firm does not enter the platform (N) and the firm enters the platform (Y). Some insights are presented as follows: We found that the firm should enter the platform if the annual service fee is relatively low, otherwise, the firm should not enter the platform. Interestingly, in the case of a firm with an offline store with relatively large operational costs or hassle costs, the firm is more reluctant to enter the platform. In the extension, we considered some consumers who only purchase offline products, and found that the firm considering these consumers is more likely to choose not to enter the platform. Moreover, we argue that the carbon tax policy has a positive effect on product prices but a negative effect on referral fees charged by the platform, and the choice of Y hurts the environment due to a relatively high total carbon emission.