Back up before the repair, not after it

The moment before you hand a machine over is the last moment you fully control your files.

Repair work sometimes involves erasing and rebuilding, occasionally it involves the very component your things live on, and quite often nobody knows which at the point the machine changes hands. Once it is gone, your ability to make a copy has gone with it. This is why the copy belongs before the appointment rather than after, and it applies even when the fault seems to have nothing whatsoever to do with storage. The point is not that anything bad is expected. The point is that you cannot act on the exception once you have handed it over.

This is doubly true when the machine is behaving strangely, because that is precisely when people postpone. There is a natural instinct to think that a copy can wait until the machine is well again, and it is exactly backwards. A machine showing symptoms is a machine telling you the window may be closing. Copies made from a slightly unwell computer are worth immeasurably more than copies you intended to make from a healthy one.

It also changes the tone of the whole interaction, which is worth more than people expect. If your things are already safe elsewhere, then the machine is only a machine, and the repair becomes a straightforward question of cost and value. If they are not, every conversation carries an unspoken fear, and fear makes people agree to things quickly and stop asking sensible questions. Walking in with your things already secured is the single best preparation available.