Elmsroth

Hello @Karibu 
You will have to modify the core on how bought items are handled.
The modfication would act as follow :
Before buying, check if player has enough space for storing the item ; Then if buy is OK, check if item is equipable ; Determine the equipment slot the item belongs to ;  Remove current equiped item on destination slot and put it on an empty bag slot ; Add the item in the destination slot (proeprty stored in the items itself to help finding the correct equipment slot) On another hand, the feature as described is not really a good idea since all players do not want to equip items directly after buying them from an NPC.
If they have big bags it will force them to search for the undesired equiped item.
Can you explain more uses cases ?
For the technical side you will find the BuyItemFromVendor method in the core in Player.cpp file.

@curatio
As it is said...in the message : DO NIOT PANIC, it is not a problem
It is explicated at the end of the install guide :
 

I will perhaps delete this message that can mislead people

Hello @Ederson Frazão,
Can you check your "account" table in the auth DB ? 
You must put the correct extension value in this field for your account. For Wotlk it should be 2.
Please consider reading DB description here to find more about this specific field : 
 
Cheers  

Or your password contains a "#"  it is a known issue at MySQL.