Mercenaries are paid automatically every hour, so you have to make sure you have enough gold to pay them during the hours you will be away from the game. The game server will deduct your gold and pay the mercs, but if you run out of gold, mercs will simply abandon you for another that can pay their wages.

Spies and agents are paid per turn unlike normal mercs that are paid per hour.

Mercenaries can only be used to attack if your reputation rating is positive. i.e. over 0. Mercenaries can be employed and used in defense at any time, regardless of your reputation score. Attacking using mercs will lose reputation. The amount lost ranges between 1 to 3 points of reputation. Depends if you attack a province smaller or larger than yourself and if you win or lose. The only ways to win a reputation point is to attack a larger target without the use of mercs, or defend successfully against the attack of a larger province. In both these cases the attacker and defender`s IP must be different or no points will be gained.