At the close of the third quarter, our nation’s seven publicly traded dealer groups collectively averaged their 25th consecutive quarter of same-store used unit sales increases.

Cox Automotive’s chief economist Tom Webb, speaking during the Manheim Index Quarterly Conference Call on Friday, says a 26th is probable, but will be a challenge to achieve.

“Slide 14 shows the seven publicly trade dealership groups and it shows that they have had 25 consecutive quarters of same-store growth in used-units retailed,” Webb said, referring to slides accompanying his presentation. “Achieving the 26th quarter will be a little bit difficult because CarMax has already reported a 0.8-percent decline in their quarter, which ends in November.

“But I still think the 26th quarter will be achieved because CarMax was more focused on supporting gross than I believe that the others will be. Which, obviously, writes in the equation, that by extension, I expect the downward sloping lines in Slide 15 will also continue.”

And the latter slide, as you probably inferred, references the used-vehicle retail gross margin for the same publicly traded dealer groups. The gross margins for used sales for the public groups is currently trending to its lowest percentage in several years — a trend Webb says has two faces.

“Now, there are two ways of looking at that gross margin trend. One could just say it’s plain ugly, and it’s dangerous,” he said. “Or, you can argue that it’s just simply the case of a competitive industry passing on its efficiency savings to the consumer. Obviously the truth lies somewhere between the two.

“But more importantly, from my perspective, I do not believe that grosses should, and hopefully they won’t, go much lower. So that means don’t look for operating efficiencies at the retail level to continue to bail out the commercial consignors. The dealers have done more than their part,” Webb said.

He says dealership proficiencies have helped that margin decline due to the lowered costs of operation that result from such efficiencies.

“A lot of that reduction in gross, I wouldn’t say was ‘willingly’ given away, but because there were tremendous increases in operation efficiencies, other dealers were able to give it away,” Webb said. “The ability to keep achieving those operating efficiencies I think are a little bit limited going forward. And certainly the benefit of exceptional growth in the throughput has probably slowed it a little bit, too.”

For more takes on Webb’s analysis, including the used-car market’s current stretch of wholesale price stability, click here.