Bought one for my wife about a year and a half ago. We both really enjoy it. However, ours shot low as well, 4" low at 25yrds. I got on Bersatalk.com in January and was directed to Colorado Gun Works, who apparently does the warrenty work for Bersa. I believe they had it for 7 weeks (not a big deal since I didn't have to pay). When Igot it back they sent a target that had the X shot up and it was noted that the group was shot with Mag-Tec ammo. There was no invoice or explination of what had been done to the gun. I have since range tested the gun and find it still shoots about 2.5" low.
For the record, I have always used a "Dead-On" site picture, as recommended on BersaTalk.com. Also, I make no clams to being a pistol shooting expert, my ablity with other handguns makes me confident that the problem is not with me.
I'm not writing this to get down on the Bersa guns (I'd buy another with out a second thought) it's just my experiece.