The use of the liquid merchant is mainly to compress emerald blocks into liquified emeralds, or to turn liquified emeralds back into emerald blocks for spending. Unlike the identifier, there is no additional cost for the transactions. Liquid merchants can be marked by a xp bottle on the Wynncraft map.
Detlas: X: 455 Z : -1580
The merchant is Detlas is found south-west of the identifier's shop, in the middle of the city.
Temple of Legends: X: -690 Z: 1010
The merchant in the Temple of Legends is near the Emerald Merchants of the east side.