Once you hit a limit, it never goes back up. I'm at 3 a day now. If you have a second character on the same account(which is where I store my dupes since banked money is shared between the 2 characters), it shares the daily limit with your first character too.
I'm not trying to be obnoxious but be sure to read the "spoiler: sell limit"(or whatever the last one is called). It will explain a lot of how the limit works.
http://www.se7ensins.com/forums/threads/everything-you-ever-wanted-to-know-about-duping.1365387/