For quality there is no specific mark, of cource Six sigma and ITIL (Information technology infrastructural library, United kingdom) are certain quality standard establishing organizations and methods. But As a normal the following should be followed:

The quality of communication, while gathering requirement, should be excellent and out standing. Some times users are just looking for a functionality in system and they are not even able to say that what exactly will be thier dream functionality which will be most convenient to them. In that case BA should explore them and figure out the exactly demanded requirements.