Unable to complete Trooper scale Pauldrons
 

The quest works up till the point you must give the potion to a froglock to make him explode. He takes the potion and gives nothing back tried invis nothing. Have done all steps 2 times.

Can't complete trades with npcs which are kos. Regarding this quest in particular, there is debate whether or not this is how it should currently function (the frogs in question are non-kos on eqlive now)

It is currently completable if you have someone charm the npc (making it indifferent con)

That is my suggestion until more evidence is found, or an alternate function is created.

I wanted to add, if you can open a trade with the slave, receive an invis, then finish the trade it should work.