There are some happy outcomes but there can be bad outcomes as well.
It's all up to how strong your dog is and how well he reacts to the medication.
Unfortunately in young puppies it is very hard on them and they struggle through the treatment and sometimes give in.
In saying that though, if you have a little battler then there is a chance he will make a full recovery, only time will tell.
I'm just preparing you for the worst case scenario.
It still amazes me how such young pups can contract parvo, but being from craigslist and from your description it is unlikley he would have had any vaccinations at all or he was exposed to the virus because the breeder just did not know anything about raising puppies.
When we have young puppies at my mums house we get doused in disinfectant before we are even allowed through the door!
We have never had a dog with parvo so hopefully someone else here can tell you exactly what to expect in the recovery.
Good luck, and hang in there.