The Farmer and a Rep

A rep came to a river crossing that he looked treacherous so he asked a farmer if it was safe to take his car through.
'Should be.' said the farmer. 'Reckon you will get through all right.'
The rep started his car and drove into  the water. After a short distance he found himself in so deep that the water was running into his windows. Extracting himself from his car, he went back to the farmer and angrily demanded to know why he had said the crossing was safe when the water was so deep.
'Can't understand it at all,' said the farmer. 'The water only came halfway up our ducks.'