First of all, no matter where you stocket, hell, nm or normal it doesn't matter.
Normal items, always max sockets.
Magic items, 50/50 chance you get 1 or 2 sockets.
Rare/unique/set items, always 1 socket.
sorry to tell every one but ganga is wrong and under the same false assumption that i had because i tried to socket a normal war axe two different times and still didnt get max sockets and after reading on the arreat summit i read that the item level as in where you found it affects how many sockets it will get. meaning that normals found in hell have a lot better chances to get max sockets than normals found in norm which i learnt that hard way.
here this is taken straight from the summit
Normal items add the max number of Sockets depending on the item's level (this is determined by the level of the monster that dropped it) and the inherent maximum number of Sockets for the item's base type. So you may not always receive the "max" number of Sockets.
Think not disdainfully of death, but look on it with favor; for even death is one of the things that Nature wills.
Ok, I guess 1 out of my 4 assumtion are wrong, here is the revision:
First of all, no matter where you stocket, hell, nm or normal SOCKETS QUEST. it doesn't matter.
Normal items, depending on the item's level to get max sockets.
Magic items, 50/50 chance you get 1 or 2 sockets.
Rare/unique/set items, always 1 socket.
What I am really interest is, what if you buy the item from npc in normal, is that consider to be low lvl and you won't get max sockets either.