Metro Trader is an achievement/trophy awarded for making deals, 10 for Metro 2033 and 30 for Metro 2033 Redux, in weapon shops. This can either be purchasing or selling weapons or equipment (e.g., filters, grenades and medkits). Ammunition trades do not count toward this achievement.
The player can obtain this achievement at any time during the missions Exhibition and Polis, since there are no more vendors after the aforementioned stations. In the Redux version, trades from Metro 2033 are combined with trades from Metro: Last Light. However, it is not difficult to get it by playing Metro 2033 alone.