Any odomoter issues with 2009 Pontiac G6 SE?

Within the last week I purchased a 2009 Pontiac G6 from Honda Of Fishers in Indiana. Today I've noticed that no matter how far I drive, the odomoter reading doesn't change. I went back to check the carfax report and noticed that it states the mileage as being 100 miles more than what the car reads. Could this mean that the dealership messed with the car to make it seem like it has low mileage? Is this something that can be fixed? And what legal recourse can be taken against them if that is the case?

Do you need someone to start your car when you go on vacation (winter)?

One of my roommates is going on vacation for a week and has asked me to start up their car and let it run for 10 minutes every day. I think they are worried about their battery? It is winter, 30 degrees F, some snow on the ground. It is a regular 2015 Honda sedan.

I've never heard of this and tried to find some articles but am not finding clear answers.

Is this necessary or beneficial to the car?

Should i trade in my honda 1993?

I have a bad oil leak which cost me to put oil in the engine ever day and a bad transmission. My car is over 300 thousands miles and i got about everything replaced in it. Is it time for me to call it quits with my 1st ever car?