Most likely, its the username. I attempted to sign up 3 times with "2003dakotart" and didn't even get a decline notice.
I would try to log in every couple of days and eventually it would tell me the account didn't exist and wanted me to sign up.
I changed the name to "1991crx" and they approved it in about a day.
also, you cannot create a new thread in the sell section until you have accumulated "Dollarz" or something like that.
basically you get credit for certain posts, or creating new threads, etc.