Perovskite quantum dots (PQDs) are known to be defect-tolerant, possessing a clean band gap with optically inactive benign defect states. However, we show that there exist significant deep trap states beyond the conduction band minimum, although the extent of shallow trap states is observed to be minimal. The extent of deep trap states beyond the conduction band minimum seems to be significant in PQDs; however, the extent is less than that of even optically robust CdSe- and InP-based core/alloy-shell QDs. In-depth analyses based on ultrafast transient absorption and ultrasensitive single-particle spectroscopic investigations decode the underlying degree of charge carrier recombination in CsPbBr3 PQDs, which is quite important for energy applications.