Twitter has posted new job listings for roles related to commerce, in a move that signals its long-simmering retail ambitions are gaining momentum. As first reported by TechCrunch, Twitter has advertised for a senior manager for commerce partnerships and a product marketing manager for the commerce team. Both will work with Nathan Hubbard, the former Ticketmaster president whom Twitter brought on last summer in an effort to let merchants sell products inside of tweets. Turning Twitter into a marketplace would provide the company with a new revenue stream, in the form of commissions on sales, and a better understanding of its users, which would benefit its advertisers.