"True" Communism?

I would like to write a brief note for would-be supporters of Marxist regimes who claim that we've never tried "true" communism in this world. That is this: when you say that there have been no true communist governments, and yet you use Marxist ideology to support, sympathize with, or defend Marxist regimes in foreign nations, I would like to know if you support these because they are "true communism" or "fake communism." 
    If you claim them to be "true communist" regimes, I'd like to know what distinguishes this regime from previous attempts at "communist" regimes.
    If you claim them not to be "true communist" regimes, then historical reference to similar types of government in the past which have succeeded would be nice. Demonstrate historical basis for concluding the superiority of such regimes over market-based mixed economy governments.