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First I would ask for the reqwuest in writing.
Second the client may be testing your integrity.
Third, if not, then maybe you cannot trust them. Also they could be relying on your integrity to really lie for them. If caught they will deny everything.
Scenario 3 is a nasty one. Will they remember how you helped them? NO they will be looking for a way to get the balance of power back in their favour. Perhaps saying you don't recall the trip is a good way out. Unless it is somewhere exotic.