We have had the blessing of only "blacklisting" a couple of website providers since we started doing SEO for dealers in 2013. Now, there's a chance we'll need to blacklist some more thanks to Google finalizing its "mobile-friendly" algorithm update.
More and more traffic going to dealership websites is on mobile devices because more people use their phones and tablets as their primary (often only) method of going online. The mobile-friendly update only affects those searching on mobile devices (for now) so some dealers have challenges and they don't even know it based upon no loss in rankings on desktop searches.
They'll see it in their traffic numbers.
In essence, the update is designed to push websites lower in mobile searches if they do not play well with mobile devices. There are a handful of things that can cause this such as small fonts, small buttons, Flash components, or basically anything that is not conducive to delivering a great mobile experience.
It's page by page, meaning that having a page that's flawed will not necessarily tank the whole site. This is good because it makes it easier to fix but it's bad because it makes it harder to identify. You need to check many of your pages, particularly inventory, video pages, and specials, using Google's mobile-friendly test tool.
This is separate from Google's 1:1 mobile:desktop search component which favors websites with pages that load on any type of device. A website can be 1:1 compliant and not be mobile-friendly; visa versa is true as well.
Thankfully, most website providers have been making the move to mobile for some time and most dealers don't have to worry, but some do. This is one of those things that can truly affect business. If you find that your website is not mobile-friendly, it's time to make a change very soon.