Auto buyers pay closer attention to advertising than most marketers assume. In the 2026 Urban Science Harris Poll Study*, 93% of U.S. auto buyers reported noticing car ads while browsing online and nearly half (46%) said these ads influence their eventual purchase decisions. The data suggests money spent reaching in-market shoppers is clearly doing so, but is it actually working?
Reaching a shopper and winning one are different achievements and the gap between them is where advertising budgets leak. Even when marketers focus on reaching “in-market” consumers, the combination of traditional targeting tactics, modeling and a platform’s ability to locate consumers means car ads are actually reaching a broader spectrum of consumers than they realize. Some are truly in-market, others may never intend to be, and others are so far down the funnel they’ve already made their buying decision. The sale may have already happened, with the ad arriving just in time to collect credit under a flawed attribution model. Those ad dollars bought a sale the dealer already owned; assuming sales were counted as an outcome at all.
The Customer’s Buying Journey
The modern buying journey makes the true impact of ad spend nearly impossible to see. Today, 44% of auto buyers spend more time researching before contacting a dealer than they did a year earlier. Consumers cross-shop brands, dealerships and marketplaces across a journey stretching one to three months, touching dozens of sites and several devices before the sale closes offline.
Somewhere in the sprawl, nearly every campaign may cross the buyer’s path and attribution reporting treats each crossing as a proof of impact. The result is a plan where everything may appear to work and wasted spend accumulates in channel after channel, each protected by its own glowing report.
To prove what ads are actually delivering impactful results, marketers need to evaluate campaign performance against a complete true outcome set. In automotive, this means ensuring the inclusion of verified sales data in the planning and decisioning processes they’re using across their channels and platforms of choice. This will establish whether a dealer’s ads are associated with conversions at all. From there, dealers can ask the harder question of what impact their marketing dollars made and how to move future spend toward what works. Answering that question is the job of incrementality.
The Incrementality Imperative
Rather than tallying which ads touched the buyer, incrementality testing asks which sales wouldn’t have happened without them and therefore where marketers are getting the largest return on investment. The method borrows the control-group logic of clinical research, where one population receives the treatment, a matched population does not and the difference between them is measured. In practice the test runs in three steps:
- Withhold a campaign from a comparable slice of the market or audience
- Run it everywhere else
- Compare actual sales between the two groups
The difference in sales reveals the campaign’s true contribution. Everything else was demand existing before the ad served, and every dollar spent claiming it can move toward ads creating buyers rather than collecting them.
Historically, marketers have been hesitant to adopt incrementality testing because they worry about withholding media from consumers they could be reaching. In reality, many of those consumers are not actively in the market, and incrementality testing can help identify where advertising is truly driving results and where it isn’t. The industry is increasingly recognizing the value of incrementality and developing more tools to help marketers put it into practice.
Meta added incremental attribution to Ads Manager in April 2025, and Google cut the minimum budget for its incrementality experiments from roughly $100,000 to $5,000, putting controlled testing within reach of dealer groups.
Automotive is now better positioned for this discipline than ever because the desired campaign outcome, a vehicle purchase, can land in sales records daily when using the right tools. Verified daily sales are what allow a test group and a holdout group to be compared against something real. Without the feed, the holdout becomes an exercise in faith.
Mazda Motor of America demonstrated the incrementality payoff during its More to Move You sales event, when it paired a Meta campaign with verified daily sales measurement and a holdout audience. The campaign returned a 3.5X incremental return on ad spend and cut the cost per incremental sale by 64% compared with the brand’s standard approach.
Building the Habit Without Breaking the Workflow
Incremental testing requires less upheaval than most teams’ fear. Choose the largest line item on the media budget, define the single question the test should answer and withhold the campaign from a comparable market or audience segment for three to four weeks while everything else runs untouched.
Measure the outcome in sales rather than clicks or leads, since lead counts inherit the same credit inflation the test exists to escape. Repeat the exercise quarterly, rotating through the budget’s biggest commitments and treat each result as the evidence base for the next planning cycle.
Expect the numbers to come in lower than the returns reported, because incremental measurement excludes the sales the store was always going to make. The discipline pays for itself in reallocation. Dollars surviving an incrementality test provably create net-new sales. Dollars failing the test move to channels actually generating demand.
Dealers can’t stop every inefficient dollar, but they can gain greater visibility into how their efforts convert to sales. Incrementality testing gives automotive marketers the proof they need to separate claimed credit from true lift. This helps protect budgets from inflated attribution and invest more confidently in the campaigns that actually drive sales.
*Source: Urban Science Online Auto-Buyer and Dealer Studies, January 2026. These surveys were conducted by The Harris Poll on behalf of Urban Science among 3,012 U.S. adults aged 18+ who currently own or lease or plan to purchase or lease a new or used vehicle in the next 12 months and 252 U.S. OEM automotive dealers, whose titles were Sales Manager, General Manager, or Principal/VP/Owner. For more information, click here.
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