Default database and default client should have compatible IDs.
Tip : Always use
Notepad++
As for items and characters,the concept is :
_Refobjcommon + _Refobjchar(connects through Link column) = Characterdata line media side
_Refobjcommon + _RefObjItem(connects through Link column) = Itemdata line media side
For the avatars problem,I'm guessing that you mean the item mall.
Shop consists of 4 tables :
RefPackageitem (same name media side) : information about the item deployment in the shop.
RefScrapOfPackageitem (same name media side) : information about the item state e.g. plus,blues etc.
RefPricepolicyofitem (same name media side) : information about the payment device(method) used to purchase the item and the quantity required to purchase.
RefShopGoods (same name media side): information about the NPC who holds the item for sale,and the position of that item in the shop e.g. first slot/second slot etc.
If the lines exists,check the service column in both sides(media and database),It's the first column and can hold values (0,1)
Also,I don't recommend copying/pasting ready-to-put stuff from releases ,it's always better to create them one by one-even if they take much time-,this way you'll get to know better about the files and to avoid crashes and errors.
Cheers