Thank you for your question. Istekhara meaning seeking the best outcome from Allah is something that is recommended to do before seeking a wife, not after selecting one. In a situation where a person has found a suitable match and is satisfied with their choice an istekhara (meaning now seeking guidance from the Qur'an) is unnecessary. Only after they have gone through the process of using their intellect, discussing with others and praying, if they are still in complete doubt then should they seek an istekhara if they wish and in that situation, since they were completely undecided they should follow the outcome of the istekhara as long as that istekhara has been taken out properly and has been interpreted properly, as indeed that was the purpose of seeking guidance from the Qur'an in the first place. A bad outcome would depend on the intention with which the istekhara was taken.
In the situation you have described a bad outcome doesn't necessarily have to do with the traits of the spouse but could be for many other reasons.
May you always be successful