Is it permissible to reject a suitor merely because of a lack of comfort with him after performing Salatul-Istikharah, even though the woman and her father are convinced of his religiosity, character, and ability to marry?

The guardian of a young woman should hasten to marry her off if a suitable suitor proposes, in accordance with the Prophet's (peace and blessings be upon him) recommendation: "If there comes to you one whose character and religious commitment you approve, then marry (your daughter) to him. If you do not do so, there will be tribulation on earth and widespread corruption." This instruction is a recommendation, not an obligation, so neither the guardian nor the woman incurs sin by rejecting a suitor for religious or moral reasons, whether due to istikhara (definition) or otherwise. As for istikhara, the preponderant opinion is that a person should proceed with the matter after performing istikhara, and should only abandon it if Allah diverts them from it.