We all know Aerys II was mad, there's no disputing that. We often see the testimonies from the nobles however like Catelyn Stark:
"Aerys . . ." Catelyn could taste bile at the back of her throat. The story was so hideous she suspected it had to be true. "Aerys was mad, the whole realm knew it, but if you would have me believe you slew him to avenge Brandon Stark . . ."
A Clash of Kings - Catelyn VII
Or Brienne of Tarth:
Brienne was still awaiting his answer. Jaime said, "You are not old enough to have known Aerys Targaryen . . ."
She would not hear it. "Aerys was mad and cruel, no one has ever denied that. He was still king, crowned and anointed. And you had sworn to protect him."
A Storm of Swords - Jaime II
But there's scarce information about how well were the people aware of their King's mental health. In fact we only see evidence to the contrary i.e. the Smallfolk loved their King like they loved his ancestors.
"Paid? He took two of my chickens and gave me a bit of paper with a mark on it. Can I eat a bit of raggy old paper, I ask you? Will it give me eggs?" She looked about to see that no guards were near, and spat three times. "There's for the Tullys and there's for the Lannisters and there's for the Starks."
"It's a sin and a shame," an old man hissed. "When the old king was still alive, he'd not have stood for this."
"King Robert?" Arya asked, forgetting herself.
"King Aerys, gods grace him," the old man said, too loudly. A guard came sauntering over to shut them up. The old man lost both his teeth, and there was no more talk that night.
A Clash of Kings - Arya VI
And Cersei Lannister's memories of the Great Tourney of Casterly Rock:
She was ten when she finally saw her prince in the flesh, at the tourney her lord father had thrown to welcome King Aerys to the west. Viewing stands had been raised beneath the walls of Lannisport, and the cheers of the smallfolk had echoed off Casterly Rock like rolling thunder. They cheered Father twice as loudly as they cheered the king, the queen recalled, but only half as loudly as they cheered Prince Rhaegar.
A Feast for Crows - Cersei V
Admittedly Aerys seems least popular when compared to Tywin or Rhaegar but people still cheered for their King.
Even the lower echelons of faith stood by the King if Prince Oberyn can be believed:
"All that," said Prince Oberyn, "and your father's fall as well. Lord Tywin had made himself greater than King Aerys, I heard one begging brother preach, but only a god is meant to stand above a king. You were his curse, a punishment sent by the gods to teach him that he was no better than any other man."
"I try, but he refuses to learn." Tyrion gave a sigh. "But do go on, I pray you. I love a good tale."
A Storm of Swords - Tyrion V
Notice that there's no mention of his madness or general unfitness to sit the throne, only that he was King by grace of gods and no one could ever stand higher than him.
Then we have what Nimble Dick Crabb, a commoner and an honest thief, told Brienne of Tarth how his people felt about Robert and Targaryens:
"And what did Crackbones do when Aegon and his sisters came?" Brienne asked him.
"He was dead. M'lady must know that." Crabb gave her a sideways look. "Aegon sent his sister up to Crackclaw, that Visenya. The lords had heard o' Harren's end. Being no fools, they laid their swords at her feet. The queen took them as her own men, and said they'd owe no fealty to Maidenpool, Crab Isle, or Duskendale. Don't stop them bloody Celtigars from sending men to t' eastern shore to collect his taxes. If he sends enough, a few come back to him . . . elsewise, we bow only to our own lords, and the king. The true king, not Robert and his ilk." He spat. "There was Crabbs and Brunes and Boggses with Prince Rhaegar on the Trident, and in the Kingsguard too. A Hardy, a Cave, a Pyne, and three Crabbs, Clement and Rupert and Clarence the Short. Six foot tall, he was, but short compared to the real Ser Clarence. We're all good dragon men, up Crackclaw way."
A Feast for Crows - Brienne IV
Here Nimble Dick isn't talking about Aerys specifically but given his age and context, he is clearly referring to either Aerys or Viserys as the true King and is proud of the fact that they are all Targaryen Loyalists where he comes from. But then again, we have Brienne's own words that she considered Aerys the true King personally, not Robert.
With rare direct testimonies concluded, if we try to judge perception of the people by the state of government, that also goes in Aerys' favour. For example:
- Law & Order: In ASOS-Davos II, Ser Davos recalls that Sea-Watches used to be death for smugglers back when Aerys II sat the throne. (Davos himself was a commoner back then). We have already seen what the smallfolk think about banditry and cruelty of Lords in Aerys II's reign in Arya's POV quotation.
- Economy: In AGOT-Eddard VI, Ned exclaims aghast that Aerys II had left the treasury overflowing with gold.
- Public bouts of cruelty: In AFFC-Brienne II, a commoner in Duskendale tells Brienne that even though King Aerys II was very cruel in punishing the perpetrators of Defiance of Duskendale particularly Lord of Duskendale's wife, Half the folk in the City agreed that the King had been too kind to her compared to her crimes and how his Grace's royal person was violated and insulted in the defiance.
- Listening to the concerns of his people: In AFFC-Jaime II, the man who killed Aerys II recalls that when Arthur Dayne brought grievances of the folks of Kingswood to the King, Aerys not only listened but also resolved their troubles.
Of course we know all of that was because Tywin Lannister was governing the realm as Aerys' Hand but the commonfolk didn't really know that (Although there were rumours that the Hand ruled the King - Which surprisingly made the common folk hate Tywin rather than Aerys because once again, only gods may rule the King). Not to mention, the Mad King was clever enough to make sure that whenever anything went wrong, Tywin got the blame and whenever things went right, he got the credit. He even actively sabotaged Tywin's reputation to boost his own i.e. he randomly raised tarrifs and duties on ports in Tywin's name, only to reduce them back graciously when the merchants, Lords and commonfolks would come begging an audience with the King to control his Hand. These people would naturally go home and talk about the hand's wickedness and the King's kindness. A most accomplished mummer, the mad King was.
Over all it seems like while the noble class and the Maesters all agree that Aerys II was a monster, the smallfolk do not appear to share their views.
How much did the public know about the extent of his madness and cruelty? I know there's nothing in the books about that since they are written from POV of nobles, have the author or his associates commented on that?