I read this on another forum so I do not take credit for this. I'm just passing this along to everyone here. I searched and didn't see this, if it is a repost please let me know, also let me know what keyword you searched for.
Here is the basics of this exploit.
You obtain 1850 and you are going for a 2350 rating to buy the next weapon. But you don't want to blow the points on the 1850 Wep then not have enough points to buy the tier 2 weapon when you hit 2350.
The catch is you can resell any item back to vendor within 2 hours. So what you do is,
1) Buy 1850 Wep
2) Que up for arena
3) Sell 1850 Wep back after one hour
4) Buy back 1850 Wep
5) Rinse and Repeat Previous Steps
6) Get to 2350 rating, sell 1850 Wep
Have the points to Buy the 2350 Wep!
9) Profit!!
So yeah if you are pretty good at arena this will allow you to get the better weapon without waiting for the points.