Slightly off topic but from an insurance point of view it's only your responsibility after work has commenced. If it's stolen/catches fire before that time then the customer should claim on his own insurance, despite being on your premises. Besides, if you haven't done any chargeable work and you dump it in the road how will he prove anything?
We once left a lotus without any wheels on the pavement outside a 'customer's' house - he wasn't too chuffed!!!
As an aside, we stopped doing warranty work about two years ago. We now get the customer to phone them up which usually means they come scurrying back a day later with credit card in hand. Most of the dealers that sell these cars know that the faults are there before they leave the forecourt anyhow. Does the phrase "just clear the codes" ring any bells?