Fiona never made contact with Tevinter. Alexius showed up in order to subvert the Mages into Corypheus' cause and even used Time Magic to arrive before the Inquisitor. Where do you think Tevinter gets it's slaves? Most countries in Thedas have laws against slavery but most of them also break them. "Slavery still thrives in Thedas, even if the trade has been outlawed. Who hasn't heard the tales of poverty-stricken elves lured into ships by the prospect of well-paying jobs in Antiva, only to find themselves clapped in leg-irons once at sea? And humans fall prey to this, too. If they're lucky, they end up in Orlais, which has only "servants." Most nobles treat them decently because they are afraid of admitting the truth. Orlesians go to great lengths to maintain the fiction that slavery is illegal." - Codex Entry Slavery in the Tevinter Imperium
Also, Alexius was part of a cult. He was lying to the Mages, had no intentions of honoring any such deal and no official support from the Magisterium.
Yes people ignore laws and sometimes don't pay the price. The point is the law existed in Ferelden. Dragon age makes it clear that Ferelden was different than Tevinter in that way.
David Gaider went further to demonstrate this in the comic "Those who Speak". When Isabella drowns a ship full of slaves because she didn't want to get caught with them. So to answer your question where do they get their slaves? They steal them from free nations. Human trafficking happens even if it is against the law.
The difference between Ferelden and Tevinter is that in Tevinter it is not a crime.
Fiona knew Alexius was from Tevinter, and therefore should have known he came from a pro slavery culture. King Alistair/Anora are not pro slavery.
You do bring up a good point:
Fiona was mistreated as a young elf in Orlais, and she may not see the difference between the nations. To her slavery was a form of life. I feel sorry for the mistreatment she incurred, but that doesn't make her a good leader. Her view was tainted by the suffering her suffering. This blinded her I'm sure.
The point I was making is she did agree to sell free people into slavery for ten years. This all occurred in Ferelden a free nation. So they clearly broke a law. What you have stated is that she had no faith or respect for this law in Ferelden. Good point, but it doesn't mean they owe her a free ride.
Your comment: "Also, Alexius was part of a cult. He was lying to the Mages, had no intentions of honoring any such deal and no official support from the Magisterium."
Correct, and we should have expected as much. He is from a different culture. Dorian stated 50% of Tevinter would have sided with Cory. That is huge. Not all these societies think the same way and that was my point. Cory and Alexius do not see themselves as villains. I was replying to a person who believed slavery was the same as a green card. It could have sounded that way coming out of Alexius because he doesn't see himself as a villain.
So it explains why Fiona a tortured women may have been easily fooled by Alexius. When Alexius took over Redcliffe she did nothing to stop him, and was still his ally. This is why King Alistair/Anora kicked them out, and ask for damages to be paid. They were very reasonable, and they could have wanted more. I would say to Fiona, "If you lie down with dogs, you get up with fleas".
Fiona is not a reasonable person, but someone who makes Big mistakes because of the abuse she suffered. I would not want this lady as a leader. Others may have seen her suffering and want to give her every chance possible. I get that. Everyone here can be a member of the jury so to speak. The fact that it is not black and white makes it an interesting story. I disband the Templars because I strongly feel it is time for a new way of thinking. Dorian Pavus is an excellent add because he provides so much more insight into another culture.