They are worth a lot ^^
Only sold on specific times, but in order to do buy goods there as trader, u have to complete a quest (1 time).
Location -> required lvl:
Jangan -> lvl 20
Donwhang -> lvl 40 (requires completion jg)
Niya Remains -> lvl 60 (requires completion jg & dw)
Roc Mtn (wind town) -> lvl 80 (requires completion jg & dw & NR)
If u buy 1* when u are 40-, u will NOT be safe!!! Thiefs can (& will) attack u !
Also, a 5* from special goods is very very hard as u always get the double spawn of a normal 5*.
So in worst case scenario, u will get 4x spawn of a normal 5*.
Good xp when it's a 90 trader, if u survive