Google's guidelines recommend minimising your categories and keeping them as high level as possible but if you wish to add more than one category you can do so in your GM dashboard.
I cannot add something as simple as "Auto Sales" in category. All of the other auto sales businesses in our town show up in that category, but it will not even appear as an option. When I type it in it says, "invalid input."
Please start your own thread providing there all information to understand and investigate your issue
This allows us to keep the forum organized and gives you the attention you need.
This ( https://www.en.advertisercommunity.com/t5/Google-My-Business/ct-p/GMB ) is our top level Community--from there, you can click into the board title that is most applicable for your issue. Once you're in an individual board, you can click on the red/pink + sign in the lower right corner of the screen to start a new topic.
And consider using "Car dealer" instead of "auto sales"
Helmut Geissler, Google My Business Top Contributor | my G+ profile