I have ATTAC 4.1.6, and I'm trying to buy/dump for Mega Robbing. Thus, I want to "anti-haggle" or, I believe haggle for "Worst Price" but the selector for best/worst/asking doesn't seem to do anything. I select "Asking Price" and it still haggles best price. I even tried turning off "auto-hagle" in the menu.

Also, what extension are custom REXX scripts supposed to be?

Yep, you found a bug. Download this zip file. It contains 2 files. Place the 2 unzipped files into the same directory as attac.exe.
When prompted to overwrite the files, say Yes and then the best/worst haggling should work properly.
earth.

http://www.tw-attac.com/downloads/BuyDumpFix.zip

I'm a developer, and I never realized I was good at QA! I guess it just depends on what you're testing.

thanks for the quick fix!

Send me any reports you find. The architecture of ATTAC allows me to update any internal script by tweaking the .erx files and no exe update is required.
That is how i am able to fix the scripts problems so quickly
earth.