Fig.: honestly, without trickery

“This is my plan. Are you in?” “I'm in at one condition: everything must be open and aboveboard. No tricks!”

“Questo è il mio piano. Ci stai?” “Ci sto a una condizione: devi giocare a carte scoperte. Niente trucchi! “

I know that used car dealers do not have the best reputation, but you can trust John. It's always open and aboveboard with him

So che i venditori di auto usate non godono di un'ottima reputazione, ma puoi fidarti di John: lui gioca sempre a carte scoperte

Aboveboard, meaning honest, dates back to the 17th century. It's a term derived from gambling, where the board is the table. Card players who do not keep their hands above the board, may be suspected of cheating by switching their cards under it