Opinion Surveys

We regularly survey area Consumers' Checkbook and Consumer Reports subscribers for their feedback on services they have used. For our survey on auto detailers, we asked consumers to rate their experiences with firms they had most recently used "inferior," "adequate," or "superior" on several aspects of service, including "doing service properly," "starting and completing service promptly," "letting you know cost early," "advice on service options and costs," and "overall performance." Our Ratings Tables show the percent of each firm's surveyed customers who rated it "superior" (as opposed to "inferior" or "adequate") on each question.

We have included on our Ratings Tables all of the firms for which we received at least 10 ratings on our customer surveys. If a firm is not listed on our Ratings Tables, it simply means we did not receive at least 10 ratings for it.

Since many firms were rated by rather small numbers of raters, small differences between two firms in the percentage of raters who gave a particular rating (say, "superior") should be ignored. The table below gives a rough guide to minimum differences you should look for in deciding on one firm over another.

When using these survey data, remember that the questions are to some degree subjective and that the differences among firms might be explained by differences in the personalities, backgrounds, critical standards, and other characteristics of the raters or by biases these raters might have.

Price Index scores

To compare prices, our shoppers made a number of calls to each of the firms included in our last full, published report and, without revealing their affiliation with Consumers' Checkbook, checked prices for basic detailing of two sedans, a minivan, and an SUV.

To compute our price index scores, we calculated an average price for each job for all the firms that quoted on that job. Next we compared each firm's price to the average. One firm might come in at 120 percent of the multi-firm average for a particular job, and another firm might come in at 90 percent. We took each firm's percentage score on each job, standardized it, and assigned a weight to each job, based on our judgment. We then averaged the standardized, weighted percentage scores to find how the firm compared to other firms overall. Finally, we multiplied this overall percentage score by a flat dollar amount, say, $100.

The price index score, then, is intended to indicate the relative prices we found for the firms, adjusted to the base of this flat dollar amount. These index scores are imperfect for various reasons: for instance, the jobs checked may not be representative; the weighting of various jobs in the index may not accurately reflect typical expenditure patterns; and the number of jobs is small.

Timeliness of the Data

All of the data must be interpreted in view of timeliness. Our customer survey data are from surveys conducted from January 2003 to December 2017. Survey respondents were asked to report on experiences in the preceding year. Our price data were collected from May to July 2010.

Our tables include firms for which we collected 10 or more ratings on our customer survey during the customer survey period mentioned above, but we do not report data for periods prior to firms' changes of name and ownership. As a result, some large firms are not listed at all. If only name or ownership changed, we do report the data. Changes subsequent to the dates listed above may not be taken into account.

Top Ratings

We give checkmarks to firms that score highest on a scoring system that we devise for each service field. Our scoring systems weight the various data in our tables and text based on our subjective judgment of their importance. Since the scores are based entirely on information presented, you can apply your own subjective judgments, and decide whether you prefer firms we have not given checkmarks. Where we do not have important data on a firm, we cannot give our checkmark.

A rough guide for deciding whether the difference between two percentages is important If one firm had this number of ratings: And a second had this number of ratings: Do not give much importance to the difference between percentages unless the difference is at least this many percentage points:
Assuming the average of the two firms' percentages is 50 percent 10
30
60
120
10
30
60
120
45
26
18
13
Assuming the average of the two firms' percentages is 80 percent 10
30
60
120
10
30
60
120
36
21
15
10