The Slave Merchant in The Rising of The Shield Hero is not a good person. Although he helped Naofumi, that was purely a business decision. That does not mean he is purely evil. He is just driven by profit, with total disregard to good and evil.
Let’s discuss below what made me reach that conclusion.
The Slave Trader: Not Exactly a Good Guy
Naofumi was struggling to survive until the Slave Trader came to his rescue. He brought Naofumi into contact with Raphtalia, was very friendly and forthcoming with information. When Naofumi leaves, he even gives a mysterious “So he really did choose her. I am getting goosebumps!”. Surely it must all be a plan for the greater good, right?
Well… not exactly. Firstly, in both the Manga and the Light Novel it is clear that the guy sells sex slaves. He also has no qualms buying “second-hand merchandise” from those who torture their slaves. The Light Novel draws an even less pretty picture: he originally planned to have Naofumi captured and sold, only changing his mind at the last moment.
So, did he change his mind because deep down, he is a good guy? Nope. He changed his mind because he believed that, in the long term, he would get more money out of Naofumi than from those that wanted to buy the Shield Hero as a slave.
…But the Slave Trader Is Also Not an Evil Person
There are also some things that speak in the Slave Merchant’s favor. He doesn’t engage in needless mistreatment and properly feeds his slaves, though that too could be seen as simply “taking care of the merchandise”. More importantly, he seems to have some code of honor as he doesn’t seem to give out misinformation or conceal things. At the very least, he doesn’t try to make himself look better than he is.
In a world where the line between right and wrong is blurred, he is simply a very morally grey character. It should also be noted that Naofumi’s reasons behind buying Raphtalia at the time aren’t quite as pure as might appear…