At the right side of the camp..
Al the way to the back..
There is a little wooden house..
There stands garrick and a female.

For those who don't have a coordinate add-on yet, or just want an extra hint, here's what worked for my lvl 5 warlock...enter the Defias area on the far right side by the river, where it meets the wall. 

Consider the area as a U shape.  Start here:
x
U

Follow the hillside as high up as you can get & you shouldn't attract much, if any, attention of those below.  At the bottom left of the U....xU..will be about as low as you will come to the Defias.  You may need to pause and wait until the current person on guard looks and walks away to continue your run.

As you continue on the bottom part of the U, you'll eventually find that the hillside contours up and that there is a path behind the hillside that will lead you to Garrick's shack at the bottom right side of the U...Ux.  Here you can pause to reflect, buff up or whatever, before you start your battle. Garrick is lvl 5 and his thugmate is lvl 3.  Both will participate in the fight.  I returned the same way I came without any problems.  Good luck!

57,48

Elwynn Forest Start 48,43.....Kill/Pickup zone 57,48....Finish 48,43

he's at 54.48

He is at 57,48 watch out though there is Garrick and another guy they both atack at the same time.

With a warrior its quit easy just rage Garrick and own him

While in the vineyard, take a look for chests. They can be found behind the cart near the bridge, close to the double huts in the South or close to the hut where Garrick Padfoot stands to the East.

Also take the quest "Milly's Harvest" to make them at the same time, saving some travelling and killing.

Why does the description above say that the quest rewards include 10 Badges of Justice?

OH GOD NIGHTMARE HOGGER!!

It really was too good to be true. The rewards are true except for the badges. No badges as reward here!
Cords for the kill is 57,48. Just east of the east corner of the field.

I don't see how he drops a badge of justice, He's too low lvl.