Switching the Location of a Mezuza

Finding a Fruit with Kedushat Shvi’it

My wife shopped at a special kedushat shvi’it fruit distribution. A few hours later, I spotted on the walkway to our building (of seven apartments) a single fruit. I took it home and asked my wife, who said it made sense that it fell from her, but asked how we can know it is not from a neighbor who might have also bought. Do I have to put up a sign or ask neighbors (whom I trust) if it could be theirs? Is it more lenient because there is no ownership of kedushat shvi’it fruit?

Tricking a Cheater

If someone asks me for an answer during a test, can I tell him the wrong answer? (Response to follow-up question – I prefer not to refuse either to not suffer socially or so the cheater gets what he deserves.)