contact the owner or the moderators. Go to the member list and visit the Moderator(s) department. From there you'd see if they are active posting in their personal profile, from which you can tip your issue at hand with the community being not moderated.
You can create your own community about the same topic, but do not expect the same engagement for some time, if ever; so try to contact the moderators and tell them your wills in helping out, to preserve the integrity of that community, instead of creating yet another car community on Google+ people won't be likely to join if there are more active communities about the same thing.
And, yes. Spammers and advertisers are going wreck-on communities lately.