I imagine that this is a typo, and they would fix it once it is brought to their attention. In such case, it is likely that there would be no liability. However, it is likely a deceptive trade practice if they knowingly maintain the price, and use it as an opportunity to talk to people who are looking at buying a car online. Check out the FTC guidance on the link provided below, these guides address this situation and provide further guidance.
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Yes, but subject to certain restrictions. Employers can monitor or completely block social media site usage on company equipment, and can prohibit employees from making statements that would be harmful to the company, even on your own equipment. However, there are restrictions. For example, an employer cannot prohibit you complaining about poor working conditions or a hostile work environment.