Simply put, they were just desperate to sell their goods.
That didn't really seem like a good explanation for the crazy way that the merchants acted, but it was the main reason why they were acting like this.
The biggest factor was the fact that they weren't able to transport their goods because of the water monster that was in the Kleen River.
As such, they had no choice but to find another way to get rid of their goods.
It wasn't enough to sell it to the villages in the surrounding area since there were only so many villagers and there were so many merchants that were here. Many of them had similar goods, so it wasn't as if all of them could sell to the villagers in the surrounding area.
At the same time, it wasn't as if the villagers would even be able to buy all of their goods in the first place.
So their only hope was the market in this town.