Netooku Otoko no Tanoshii Isekai Boueki (Light Novel)

The Netooku Otoko no Tanoshii Isekai Boueki light novel series was first released in web format by Kon Hoshizaki. As of 07/11/2011, 164 full chapters were released online completing the story, and seven complete volumes have been published by Media Factory. Sazanami Mio illustrates the published novels.

Synopsis
Ayase Jirou is someone who makes a living by net auctioning things he purchased from people who don't need them anymore, in other words a "Picker." One day, he found a large antique mirror from an old bag's cellar which was given to him for free. That mirror is actually a portal to another world, allowing him to go back and forth between worlds, much like Kakedashi Programmer. In no time he found an exploit that by selling things from modern world to the other world and vice versa he could get filthy rich in no time at all!

Resources
There are some notable differences between the web and novel versions. As of the moment, the web version is still being updated. However, translation projects for the novels appear to be focused on the published versions.