People have been talking about if the 270 is big enough.. sure it is, Just educate the hunter on the bear as was noted in earlier posts. the most common mistake people make bear hunting is that they shoot too far back because of the thick fur, with a black you really need to look to find the back of the shoulder, know where it is don't guess. There is nothing I hate more as and outfitter than to track wounded bear that someone gut shot because they where in a hurry to shoot, or where uneducated as to where to shoot.
I would suggest that any new bear hunter going on a guided hunt should ask that the guide spend the first and maybe second night sitting with the hunter to help pick a bear, place the shot, and maybe calm his nerves. Any outfit that won't accomodate you in that regard, is not wrth dealing with, because they are not there for you. Alberta is nice for this reason.. I will take a first timer out if he requests the help, most want to do it on their own, but I will go, or one of my guides will go. The hunter can take a bear the first night with the guide, build some confidence, then hunt the second bear on his own. Most times guys will shoot the first bear they see, and it usually is a dink of a bear, second tag they can be more choosey.
The other part of the post said that you where using a 300, I hope with your 300 you use a light load. I have seen many hides almost destoyed buy 300 cal rifles.