Li Du thought that Conrad was a bit foolish. He had just made the worst decision. Bell had tried to be the middleman. Conrad had two of the best options. The first was to give Bell respect and give up bidding. This way, Bell would have owed him a favor. The second option was to keep his dignity, not give Bell respect, and fight Li Du all the way. In the end he chose a third option. He increased bidding and made Li Du furious. Only then did he quit bidding.
This meant that not only did he not give Bell respect, but he also did not successfully defeat Li Du by winning the storage unit. He had wasted his energy and pissed off someone at the same time.
Of course after he gave it some thought, perhaps that was not the case. In Conrad's eyes, he had made the best decision. He had given Bell respect when he quit bidding, and in the end, he had made the price even higher. Even though he could not defeat Li Du, he could piss him off.