I think they usually do the left arm, most people are right handed...
But I've had this problem before, usually if you ask for a specific arm, or present a specific arm they'll take that arm (if they find a vein)
I wouldnt worry about it...
Even if they see the scars they dont usually react. I've had this done several times by several different people, and none of them have ever reacted to scars (or even fresh cuts...)
I have noticed that they take blood from the arm that has a vein that is easier to get to. A while back I went to get my blood taken and I had cut all up and down my arms but no one said anything and I didn't get into trouble. If that is something you're worried about than don't be. =)How do I stop scarring
It depends where they can find a good vein. Tell them you would rather have it in your right arm. They usually will listen to you and do it where you want it.How do I know if my arm is broken?
it depends they'll probably do your right arm though. just ask them to do your right arm if it gets down to it.What does scar tissue under the skin feel like?
then tend to take it from the hand you use less.
so left for a right -hander.