After getting Asassin's dagger if you say payment again scanthril tells you that somewhere north from where he is,you will find his hideout and you should say "Scanthril" to the rogues in there.Now,i couldn't find any hideout and i wonder if someone knows anything about it.
Another thing : i used to advance very quickly with my characters just by learning different magic levels and buying the needed books at the appropriate guilds.The problems is that right now i am offered books very rarely and i wonder what's happened.

Certain books are only offered at certain levels and only by certain guilds. Let me see if I can remember them:

Wizard Guild: offers
Burn
Torchlight
Blinding Flash
Flamedrop
Illuminate
Dazzle
Reveal
Incinerate
Circle of Fire
Shock
Armorplate
Melt
Zap
Armored Realm
Negate Magic
Lavawalk
Dementia
Frighten
Nimble
Sleep
Freeze
Invisibility

Thieves' Guild offers:
Shadow
Bloodlust
Pain
Frenzy

Priests' Guild offers:
Bless
Heal
Awaken
Charm
Spirit Eye
Heroic Might
Healing Realm
Slow
Repel
Stink Bomb
Haste
Lure
Pry
Toughen
Unbind
Cure
Breath of Air
Vanish
Create Portal
Call of Home
Twisted Master

These are all I can remember. You have to be at the appropriate spellcraft level to buy the book. It won't be offered if you a) are at a level below the level required to learn the spell or b) if you already know the spell. It also won't be offered if you are in a class that no longer supports knowledge of the spell (e.g., Samurai by nature can't learn Spirit Magic, although if you already have Spirit Magic, you can continue to develop spells...but you won't be offered any more books in Spirit.)

-Sazerac

Wow, another impressive feat from our photographic memory! Strange though that you can buy the create portal spell, but not the teleport.

Hideout = boogre caves; just a nice place to get rid of people too curious / greedy.

are you sure ? I didn't get the impression that this hideout is the boogre cavern.

Yep - it's the Boogres Cave - he's just trying to ditch you.

Wyv