The good news: every visitor that your vendors send to your website can be tracked through Google Analytics. The bad news: it doesn't happen automatically.
In order to see the true number of visitors from vendors that send your site a substantial amount of mobile traffic – like Cars.com, AutoTrader, and Pandora – all the links pointing to your site need to be tagged to play nice with Google Analytics.
As smart as Google is, it can't detect the source of a visitor arriving from a mobile app – and neither can any other analytics tool.
Instead, Google Analytics will label it as a "(direct)" visit in its reports, which means it won't show up when you look at Cars.com and AutoTrader referral traffic. Pandora traffic is an even bigger issue, since the traffic it sends is almost entirely mobile-focused – typically at or above 90% – and a huge chunk of it will come through the mobile app. So unless it's tagged, you're unable to see the impact of that traffic.
The same issue applies to social campaigns. Dealers engaged in any kind of Facebook or Twitter marketing with the end goal of getting those visitors to your site need to tag social links so that mobile app visitors aren't getting lost in the catch-all "(direct)" dumpster. Basically, if you have any vendors or marketing channels that involve a mobile app, you want to make sure all links to your website are tagged appropriately.
There's a little more good news on the way: tagging URLs is easy. Google even has a convenient page dedicated to it, and we'll run through a quick example of how to use it.
First, enter the URL of the page that you're linking to. For Cars.com and AutoTrader, this will typically be the homepage. For Pandora, we highly recommend this be a (mobile-friendly!) page focused on the offer that you're advertising.
After that, set the Campaign Source to the site/company that's sending you the traffic. Then, make sure the medium is set to referral so that Google Analytics knows how to categorize it. Let's use the Cars.com link for the fictional Bruce Willis Honda of Hollywood as an example:
Notice that this matches the source/medium format of Cars.com traffic currently appearing in your Google Analytics reports:
By keeping the source and medium the same, you'll have all of the cars.com traffic included in a single row within Google Analytics whether it's coming from the website or the mobile app. This will make your analysis simpler.
There's one final field that Google's URL Builder forces you to include, and that's the campaign name. For referral traffic from Cars.com and AutoTrader, you don't need to worry about it. But for other digital channels where you shift the messaging frequently or adjust the type of advertising you're doing, then the campaign tag comes in handy to see what worked best.
But for our Cars.com example, we're just going to put "test" as the campaign name so that we can use the URL Builder. From there, hit the Submit button, and then copy the URL that's generated for you, but leave out the &utm_campaign=test part:
Paste that link into an email to your Cars.com rep and ask that they use that for all links across their desktop site, mobile site, and mobile app.
After that, do the same for AutoTrader, Pandora, Edmunds, and any other referral site/digital channel that you know sends traffic to your site through an app. For Facebook and Twitter, work with the agency that handles your social marketing to make sure that the links to your site are tagged. You may also want to consider campaign tags for social links to see which types of content are driving the highest-quality traffic.