artless
She's a wizard with numbers and also artlessly articulate.
His architecture artlessly combines new and old without the slightest hint of irony.
In this new book the writing seems artlessly conversational.
No one could deflate a person or idea more artlessly and devastatingly than Mrs Roosevelt.

SMART Vocabulary: related words and phrases

Honesty, openness & sincerity
(as) man to manidiom
above board
anti-corruption
artless
artlessness
earnest
honestly
in all honesty/seriousness/truthfulnessidiom
in good faithidiom
integrity
joking apart/asideidiom
let's face itidiom
sincerely
stainless
straight arrowidiom
straight upidiom
straightforward
the straight and narrowidiom
transparency
upright