Agressive Biting in Puppy!

Question
I just recently bought a 9 week old golden retriever from a pet store called Just Pets, which I would NEVER reccomend anyone to do.  My family has had a horrible experience with him because he is constantly biting.  We cannot even pet him without him biting and sometimes drawing blood.  He will bite hands, legs, feet.  He has chew toys and we have tried all obiedence/pack leader methods all of which have failed.  His behavior just gets worse.  Is this something that normal puppies do?  Or has he been mistreated and improperly socialized by breeder?

Answer
Pet store puppies are often removed from their litter too soon making the problem worse, but it is still very common in others.  

Young Labs, which I know best, and other puppies tend to very bad about
biting.  You see a litter of them, and all the ones that are awake are biting
another one or themselves.  I am not even sure they realize that when they are
alone, if they quit biting, they would quit being bitten.  At 3 to 4 months
they are getting their adult teeth, and it seems they spend every waking
moment biting or chewing.  One thing you can do at that stage is to knot and wet a piece of cloth.  Then freeze it.  The cooling will soothe the gums.  Only let the puppy have it when you are there to watch it.  I maintain a Lab's favorite chew toy is another
Lab.  Otherwise they settle for any person they can.  They keep hoping to find
one that won't yelp and jerk their hand away, or growl "Bad dog." and clamp
their mouth shut.  Then offer a chew toy.  They keep trying despite hundreds
of corrections.   Another good technique is to yell ''Ouch!'' and quit playing and go away.  Be sure to praise them when they are playing nice and not biting.

You just have to keep on correcting them, hundreds of times, not dozens.
Provide sturdy, safe toys such as Kongs and Nylabones.  Avoid things they can
chew pieces off and choke on them.  Keep them away from electrical cords.
Crates are essential for most young Labs and other dogs.  

The pet stores are full of toys that many dogs will quickly chew up into
pieces they could choke on or cause intestinal blockages.  If you are not
there to watch, stick to sturdy stuff such as Nylabones and Kongs.  Keep a
close eye on chew toys and quickly discard anything that is coming apart in
pieces.  Rawhide is especially bad because it swells after being swallowed.
These problems are the worst with, but not limited to, large, aggressive
chewers such as Labs.