A host of mystery shoppers sent to critique dealerships across the country gave luxury brands such as Mercedes-Benz and Lexus high marks and put Ford and Lincoln above the industry average.

The study of dealerships, released Monday, also found that fewer salespeople offer vehicle brochures that customers can take home. Only 57 percent of dealerships offer brochures, compared with 62 percent in 2007.“I’m absolutely certain that paper brochures help sell cars,” said Fran O’Hagan, chief executive of Pied Piper Management, which is based in Monterey, Calif., and conducted the study.

Now in its fourth year, the study aims to help automakers and dealers determine how to boost sales. Improving the experience at dealerships is essential at a time when they are recovering from a loss in numbers.

Moreover, dealers may have to work harder to sell cars during the second half of the year, as many potential buyers may still be holding off.

Pied Piper’s study zeros in on tangible things a dealership can do to influence a sale.

The firm deployed 3,658 secret shoppers, age 21 to 65, to dealerships between July 2009 and June 2010 to collect more than 50 observations, such as whether a salesperson:

– Asked how the shopper would use a new vehicle and who would be driving;

– Offered a test drive;

– Was knowledgeable about the product.

Using that data, Pied Piper gave each brand a score and a rank.

Lincoln’s score jumped 4 percent, more than any other brand, compared with 2009. Lincoln’s salespeople were more likely to talk about a vehicle’s features and ask why the shopper considered the brand.

O’Hagan said salespeople need to do more to involve shoppers, such as finding out more about a customer’s needs and walking a shopper around a car, pointing out important features.

Salespeople, O’Hagan said, need to “engage the shopper in some way that isn’t just me lecturing them.”