You may trust all those you give keys to, but others may have had access to keys before you moved in, or while the house or flat was vacant.
I resecured a house recently after a few ‘strange occurrences’ that made it clear that someone was letting themselves in. The owner was adamant that he had never heard of such a thing in his 40 years renting out property, but the tenant had evidence. Who it was? No idea. But they won’t be getting in again.
In another case, expats returning to the UK traveled over with their removal firm, supervised the unloading and locked up before returning to close the sale of their overseas property. On their return, boxes had been owned and rummaged through – clearly very distressing, & at the time I was changing their locks, they had no idea what may have been taken!
So, get your locks changed as a priority when you move.