Were there any hints that this character was the Power Broker?

One way of addressing this without resorting to hindsight is to review articles theorizing about the Power Broker's identity before the reveal was made.

Phil Owen of The Wrap theorized that the Power Broker could be Baron Zemo, Batroc, or Sharon Carter, with Sharon being the most likely. The evidence that Owen marshals is as follows:

• If Sharon is capable to quickly building a black market art enterprise, she is capable of doing much more
• That enterprise, and her massive home, and her armed guards are all potential clues — it wouldn’t be shocking for somebody who has “broker” in their name to have an illicit art business.
• And you absolutely would expect a crime boss to have an extremely nice house with a bunch of guards.

Thomas Hitchen of Inside the Magic added more observations in a similar article:

The suggestion is that Sharon Carter is the Power Broker, that her time since the Avenger’s Civil War has changed who she is and what she is willing to do to get by. Carter tells Wilson, Barnes, and Zemo that she’s managed to survive by selling stolen artwork to high powered criminals in the city. She also seems…pretty well off. Which is fortunate in a way, seeing as though Cap’s squad pretty much forgot about her. Not only does she seem to have the political weight to move freely throughout Madripoor, but her insider knowledge of the syndicates who work the streets is detailed. She is confident when we see her again, seemingly woven into the very fabric of criminal society. This theory takes on a new light by reevaluating the meaning behind Carter’s last words in the episode, when she says — “We’ve got a big problem. Actually, a couple of them.”

Grace Wehniainen at Bustle spotted an important coincidence:

Sharon’s been hiding out in Madripoor since helping Steve and Sam escape during their very illegal quest to protect Bucky. Here, she is at least living well as a very connected art dealer. As she tells Sam, “at some point I thought if I had to hustle I might as well enjoy the life of a real hustler.” She agrees to help the group find Nagel (whom she recognizes instantly as an associate of the Power Broker) and very quickly does just that... almost too quickly, perhaps.

Finally, Thomas Bacon at ScreenRant spots an anomaly of episode naming and an obscure link via the CIA:

But episode 3 is titled "The Power Broker," when at first glance the character doesn't even appear but instead is only discussed and alluded to. Unless, of course, the title will take on deeper meaning with the benefit of hindsight, with viewers realizing they've been introduced to the Power Broker in secret – because this is the episode that brings Sharon Carter into the series.

Wilfred Nagel [...] found the CIA had pulled all funding from its super-soldier programs. Frustrated and embittered, Nagel found his way to the Power Broker. Curiously enough, Sharon Carter also briefly worked for the CIA after the collapse of SHIELD.

Who raised the bounty?

If Sharon Carter placed a bounty on her own head alongside those of Sam and Bucky, then that really was an extraordinarily deep deception. But it also provided cast-iron cover (the bounty hunters really were trying to kill her, which supported her position as an ally of Sam and Bucky). But it is not certain that it really was the Power Broker who raised the bounty.