The first thing to determine is which eye is dominant. Some lefties are right eye dominant, and vice-versa. Either hand can be trained to use the action, but you'll always pick up the sights better with the dominant eye. There's a lot of right-handed people who would be better served by a left-hand gun.
To determine dominance, focus on a distant point. Overlap your hands, leaving a small opening between the webs. Bring your hands up, arms extended, into your line of sight. Close the left eye. If you still see the point you focused on, you're right eye dominant.
Some stocks exhibit "cast-off". The stock is angled slightly to the right, and snugs up nicely for a right-handed shooter. These are horrible for a lefty. Look straight down the gun from the muzzle, to see if the buttstock is straight or angled.