I'm no expert, since Tomoyo is our very first fuzzbutt, but she is the
most laid back ferret I have ever seen.  When we got her home, she'd only
play for half an hour or so and then needed a nap.  Needed as in she'd
fall asleep in our arms as if to say 'ok, you've worn me out'.  If this
is a very young ferret and has around the same temperament, he'll probably
do a lot of sleeping.
 
All I can say is that I've noticed, by having Tomoyo, that ferrets have
a lot of the same behavioral patterns as dogs.... dogs that are way too
curious. ;)  Most puppies will sleep away a good portion of the day.  Now,
Tomoyo's active time is in the early morning and in the evening.  It could
be that the folks in the pet store just aren't there when this ferret is
ready to play.
[Posted in FML issue 3776]