Castles was found guilty of five charges relating to gross overcharging, general conduct and serious failures in professional standards. Three other charges were dismissed.
His penalty has yet to be determined.
Meanwhile, another recently released tribunal decision stated the reasoning for striking off a lawyer who was found guilty of misconduct in October.
Evgeny Orlov was struck off the roll of barristers and solicitors, in part because of unfounded allegations he made against High Court judge Rhys Harrison in 2008.
Orlov stated Justice Harrison's attitude and statements showed an apparent bias "not only against me but against the political beliefs that I hold''.
The tribunal's decision stated that in the course of his five-day hearing before the tribunal Orlov used "extravagant and insulting language'', compared the tribunal to the Spanish Inquisition and a Stalinist show trial, and accused it of creating an atmosphere that existed in Nazi Germany.
"His approach was vexatious, insolent and provocative,'' the tribunal's decision stated.
Orlov previously represented former Zion Wildlife Garden operator Patricia Busch during a long-running feud between her and her son, `Lion Man' Craig Busch.