If you are trying to get a person to like you that has the persuasion option when you talk to him you can incrase the maximum disposition level a little bit more.

I've tested this trick out myself with some Imperial city gaurds and it works as long as you keep trying with the person until you reach the "Disposition Maxed" message on the persausion menu.

All you need to do is talk to the person you wish to persuade with your weapon DRAWN and then get him to like you through the persuasion ability until the menu says "Disposition Maxed."When you do that, simply stop talking to the character and put your weapon away, when you then go to the persuasion menu and look at the disposition level you will see it is somewhat higher(I believe the maximum posible disposition you can achive through this secret is ten). The amount you can get from this seems to depend on the NPC's persuasion level and your charcters persuaion level and the NPC may have a grudge with you or a bond with you from things you may have done to help or hurt them or your charcter may have infamy and/or fame, or the guild you belong in and your curent rank in that guild may affect the way this person feels about you.

I must also warn that certain charcters aren't possible to persuade mainly charcters involved with quests, (For example Baurus of the Blades.)