Maybe this is an urban legend, but:

Sinclair Research made early home computers, well known in the UK, not so much elsewhere. These were tricky to set up, and often returned as broken. To cut their support costs, supposedly Sinclair, on first receipt of a 'broken' computer would simply add a sticker and send it back, 'repaired'. Often the customer would get it working on this second attempt. Only when a computer was sent in with this sticker already applied, would they actually investigate to see if anything was wrong with it.