my job

I work in an exporting company who help foreigners buy goods from China`s online stores. Speak definitely,it is a purchase agent.Many foreigner like china`s goods, they are cheap and their quality are good

I work in an company which helps foreigners buy goods from China's online stores: a purchasing agent. Many foreigners like China's products as they are cheap and of good quality. 

Also, it might be more idiomatic to say "I work for an exporting company". However both prepositions are acceptable.

I work in an exporting company which helps foreigners buy goods from China's online stores. In otherwords, it is a purchase agent. Many foreigners like Chinese goods, because they are cheap and good quality.