The licence is valid as long as the requirements are met – but the Transport Agency reviews continuously and can warn or revoke.
The taxi driver licence is not something you pass once and then forget – it is valid as long as you keep meeting the requirements on driving ability, health and good conduct. It also ties in with your driving licence: if you lose your licence category, it affects your ability to work as a taxi driver.
The Transport Agency reviews your suitability not only at application but on an ongoing basis while you hold the licence. The authority can receive information about crimes and other circumstances and weigh them into the assessment. The point is that the good-conduct requirement does not end the day the licence is issued.
If you are judged unsuitable, the Transport Agency can either issue a warning or revoke the licence, depending on how serious the matter is. Grounds can be crime, no longer meeting the medical requirements, or the driving licence being revoked. A revocation means you may no longer drive a taxi until you possibly meet the requirements again.
The best way to keep the licence is simple in theory: drive safely and lawfully, keep your driving licence valid and make sure you continue to meet the medical requirements. If you carry out the profession responsibly, the licence is a long-term asset that follows you through your working life.