The "Doujinshi" refers to the magazines or publications produced by individuals/associations, which are the self-published books, while the Shougyoushi is different from the Doujinshi, it is a kind of book that the publisher pay for the author to write.
Since it is Doujinshi, the "re-creation" is very important. The general comics are original works, so they are the "one-time creation", but the Doujinshi are the works based on the original creation, so it is called the "re-creation".
As mentioned before, the Doujinshi is not published through publishing houses, so it only contains the information such as title and author's name. Please be sure to pay attention to this point toward buying!
What do you think? After reading this article, you should not have to worry about how to distinguish the Shougyoushi and Doujinshi when buying it! When you make a good distinction between official or fan-made work, you can enjoy all the moments of reading!