The spirit militaries Xu Jialing showed Qi Tian were all of heavenly level, and the Heavenly Dao Engine's reaction to them was tepid. This indirectly confirmed that the Red Hoop Stick which excited the Heavenly Dao Engine so much, must indeed be a great item, and likely an exceptional one at that.
Since the Heavenly Dao Engine's response was neutral, Qi Tian decided to pick the inner armor on his own. He could consult Huang Liuyan, so he was not worried about buying something of poor quality.
Qi Tian made his selection carefully. Although he still had some spirit stones, he needed to keep some for his own cultivation, so the spirit stones he could spend on inner armor were very limited.