to haggle, to bargain

solemn, stately, serious

earnest, serious, real

standard, adhering to regulations

to make a modest remark, to speak modestly

motivated, self-motivated, self-starting, proactive

to take the initiative, to take it upon oneself, to do something on one's own accord

initiative

to reason with someone, to talk sense into someone, to argue

to discuss the merits of an argument