shares of carscom sank thursday after pretax income fell in the second quarter the stock was down 16 to 1880 premarket shares have risen 63 so far this year the chicagobased online carseller reported a second quarter profit of 941 million or 137 a share compared with 555 million or 8 cents a share a year earlier the companys profit surged on a 931 million tax benefit and pretax net income fell to 105 million from 628 million a year earlier carscom said that its dealer customers declined compared to the first quarter of the year falling to 18785 from 19186 average monthly unique visitors fell slightly from 271 million last year to 269 million