The odds
After seeing how Innu reacted after finding out about what the V were, Quinn had been sure that most other people would share his underlying fear of the V. So much so that he never imagined that Sach would voluntarily ask to be turned.
Unfortunately, there was an underlying problem even if Quinn did agree to Sach's request. He had plenty of spaces left to turn others, numbering 18 as of now. Whenever someone Quinn had turned died, one of the available slots would return to him as well. Turning Innu hadn't caused any problems in that department, but the troublesome fact was that he had no way to control what Sach would turn into.
'You were a little lucky when you turned Innu, but you can't guarantee that Sach will turn into a vampire as well. He could turn into something else.' Vincent cautioned Quinn, just reconfirming his worries.