As seen in the trailer for Thugs of Hindostan and the movie, Khudabaksh (Amitabh Bacchan) and Firangi (Aamir Khan) share this dialogue
Firangi: Dhoka mera swabhav hai (Deceit is my nature)
Khudabaksh: Aur bharosa mera (And trust is mine)
Khudabaksh reiterates his trusty nature through several similar dialogues in the film.
Even though Firangi infiltrates the rebel Aazad army and gives up their location to Clive of the British East India Company, Khudahbaksh entrusts Firangi with the amulet to protect Zafira and the rebel army.
However, earlier in the movie, when another spy is brought before him, Khudabaksh beheads him even though the spy asks for forgiveness and another chance to prove himself.
So why did he behave inconsistently? Why did he choose to behead one spy while trusting and giving another chance to another spy (Firangi)?