Hansam and buck460XVR have given you some very sound advise. The only thing I can add is to look at the pedigree, if it is stacked with lots of field champions you are going to have a very high energy dog, if the pedigree is stacked with AKC show titles you are more likely to get a mellow dog, not certain, but more likely. As a general rule I have noticed this trend with dogs that we breed and have begun to use it to our advantage.
Likes buck460XVR said a quality breeder is of the utmost importance. Nothing is worse than getting attached to a dog only to find out is has a liver disorder and watching your dog have seizures for the rest of its life or wind up having bad hips or some other problem. I have talked with a lot of people who have had this problem and it is hart breaking for them.
You can probably guess from my user name that I breed labs, and we put a lot of effort into insuring that the pup we supply has the best chance of being a happy healthy dog that will fit with you and your life style. If I don't think I can supply what you need and want in a dog I tell you right up front. A dog is a very long term commitment and it needs to be right for both of you.
This last winter I started looking for a upland dog and was seriously considering a GSP until I did some investigating. The first red flag came up when I started talking with the breeders here in Idaho and Utah and all but one had no idea what I was talking about when I started asking about health clearances.
The second and final came up when I consulted my vet and she informed me that the breed is known for having some temperament issues. While not every dog is going to have issues, she has seen enough of it that she felt concerned enough to say something to me. She said the ones that have problems either start out with them or they develop them as they age. I can't help but believe that this is yet another issue resulting from the incredibly poor standards set by the AKC, the only minimum standard is that both parents have papers.
It appears that some of the posters have experienced this range in temperaments from first class dog all the way to having to put one down.
I would not take getting a high end hunting dog lightly. If they are true hunters you will have more issues than you know what to do with.
By the way I settled on getting a Deutsch Drahthaar, they are the German registered version of a GWP. The breeding standards are very strict.
I do not mean any disrespect to your friend but if he is not a regular breeder then you really need to get a copy of the pedigree and go visit with a reputable breeder before taking a pup. You should also spend some time around the parents and make sure that they acceptable. If you have any questions or concerns please contact one of use and ask away. Its way better to find out know before its to late.
* (Swinging club) Whack! whack! whack! *
Nope, the old nag's still dead .