Agreed. In fact, I wouldn't even pay what it should have been. If you do that, then the driver has nothing to lose by being dishonest. His downside is what he would have earned anyway.

If the driver tries to rip you off, offer him half of what the fare would have been. As documented elsewhere in FT (by me, among others), the threat of summoning the police often helps smooth any negotiation. Perhaps then he will consider his approach with the next passenger more carefully. As with many things in life, one discourages undesirable behavior by attaching a cost to it.