Is the testimony of a manager or colleague regarding an employee's accomplished work, intended for reward, increased trust, or motivation, considered blameworthy praise if it is truthful and sincere, and does its ruling differ from that of [giving] thanks?

Praising a doer of good and encouraging him by acknowledging his excellent work for a commendable purpose is not blameworthy flattery. The Prophet, peace and blessings be upon him, praised the Companions when he said to them, "You have done well," or "You have hit the mark," because they performed the prayer at its prescribed time. Praising a doer of good to encourage him and urge him to do more good is not blameworthy; rather, it is considered just. However, exaggeration and overstatement in praise are not permissible, nor is praise permissible if there is a fear of temptation for the one being praised. As for thanking people for their kindness, it is enjoined, for the Prophet, peace and blessings be upon him, said: "He who does not thank people does not thank Allah."