grammatical number - Can 'nothing' ever be preceded by a plural verb?

I've had it drilled into my head that nothing is always singular, since it's essentially another way to say 'no thing'. However, in the following sentence, I'm having trouble ascertaining whether the preceding verb should be singular or plural:

There are nothing but liars in here.

Is this sentence acceptable? I'm inclined to believe that nothing is being used as an adverb rather than a pronoun, so it is correct to use 'are' rather than 'is'. Here's another example sentence:

They are nothing but petty thieves.

In this case, since the subject is simpler, it becomes more clear that the plural should be acceptable. Am I understanding this correctly?

Answer

The are applies to liars, not to nothing here.

Did you notice that you have but in both your examples? Nothing but as a phrase is used here in an idiomatic sense. We can reread the sentences as:

There are only liars in here.
They are just petty thieves.

That's how it is, I believe.