Why was the questioner guided to work for a company that he later discovered practices deception, despite having performed Salatul-Istikharah before traveling to work for it?

The expansion or contraction of the chest of someone performing Istikhara prayer are merely speculative indicators. Moreover, the inclination towards an action might precede the Istikhara, leading one to mistakenly believe it is a result of it. If an action is Islamically forbidden, then its choice cannot be attributed to Allah, as the flaw lies within oneself.