Here's my theory on lapping people:

Aim for them!

By the time you get there, they will be somewhere else and you'll go right by. Keep in mind this only goes for those racers who don't have the control it takes to let you by cleanly. Any racer that is capable of holding a line shouldn't be a problem to pass. If you put a move on someone and they punt you in the next corner, you need to have a chat with them after the race to explain courteous driving.

Scenario 2 goes something like this:

Any battle for position should be respected. Doesn't matter if the battle is between 1st and 2nd or 4th and 5th. Don't mess with the battle. As an example, last week I was racing and the leader managed to get a lap lead on the field and came up on the battle for 2-4. The leader then slowed a little to not interfere with the fight for 2, 3, and 4.