If this is a house that you really like, I wouldn't mark it off the list immediately. Movement in the ground is so common in Mississippi that there's a good chance that quite a few houses that you see will have the same problem. You didn't say if the crack was a dime size or if you could stick your hand in it.
Usually the owner of the property will pay for you to have a engineer report done to determine if the property really has issues or that the house has just settled. If it is an older house, then probably it has already done what it is going to do. You can ask for past records to determine if it has had to be fixed before.
According to the MS Builders Association, on a new house, builders are required by law to fix any issues up to 7 years after being built. The key is finding out who the Builder was and is he reputable.
There are definitely areas that I would stay away from. If you walk through the house and every few feet the floor is moving up or down from room to room, then most likely that will never be completely fixed.
If the whole house or a particular room is leaning down hill in one direction, usually the house can be lifted on that low end and you can't tell it ever had a problem. Sometimes you can get the sell to fix it prior to purchase.
If you don't feel anything in the floor at all, have the seller supply a valid report of clearance and just fix the morter in the brick. There are tons fo great houses out there with fixed morter.