What is the ruling on agreeing with a recruitment office for a maid's salary of 850 Riyals while her contract with the office states 800 Riyals, and should the maid be given 800 or 850 Riyals to absolve oneself, knowing that she is unaware of the office's contract?

If the recruitment office acts as an agent for the maid and agrees with you on a specific wage, then you are obliged to pay it to the maid unless she waives her right. However, if the office does not represent the maid but rather signs perfunctory papers, then the considered wage is what you agree upon directly with the maid.