I havent read the book but I saw a summary where it stated MC traveled between two worlds and traded/sold merchandise. Do you know the title?
http://www.novelupdates.com/series/jikuu-mahou-de-isekai-to-chikyuu-wo-ittarikitari/ http://www.novelupdates.com/series/takarakuji-de-40-oku-atattandakedo-isekai-ni-ijuu-suru/ http://www.novelupdates.com/series/isekai-c-mart-hanjouki/ all three have a similar back and forth between worlds with trading involved as well (to varying degrees) but it's probably the netooku one above