It is unlikely to steal, but it is very easy to replace with used spare parts. A battery, for example, a Chinese battery with a lower capacity, a second-hand display, etc.
If you want to protect yourself from such incidents, look for specialized service centers where everything is repaired exclusively with you personally.
If they take out memory, motherboard or something else while your iPad air is being repaired, then it will not work later. But you will check upon receipt, at least try to turn it on !?