I have also seen some labs that show no point when young and then start pointing when they get a little older. As far as a guarantee, I known of very few that would give that kind of guarantee for any breed. Reason, let most breeds of dogs start catching planted birds while training and see what happens, Esp. in labs and your versatile breeds. In my opinion if you are in the business of selling dogs anything you can do to better the breed you should try to do it. Again in my opinion, if you are in the business, you should stand behind what you are selling.
Most breeders have contracts that guarantee the pup if there is a problem.
Most of the kennels that I know want to know if there is a problem and more than willing to help. No, it is not true, I know there was an article done on labs that point, that said that pointing could hurt the dogs desire to retrieve by a professional trainer, and writer. Bottom line retrieving is something that takes place after the point, the pup is still a lab if it doesn't retrieve, but he won't be invited for dinner at my house. Yes, I believe a lab could be trained to point, hesitate, or hold on a bird. There is a person who advertises in the field that trains labs to do the above.