How could Merry know about who "Sharkey" was just before he showed up in end of The Return of the King?

Question

Merry looked round in dismay and disgust. 'Let's get out!' he said. 'If I had known all the mischief he had caused, I should have stuffed my pouch down Saruman's throat.'

'No doubt, no doubt! But you did not, and so I am able to welcome you home.' There standing at the door was Saruman himself, looking well-fed and well-pleased; his eyes gleamed with malice and amusement.

Source: The Return of the King, Book VI, Chapter 8.

I just read this part (in a physical book, 2005 Swedish translation), and it confuses me.

While they do meet Saruman on their way homeward, and his name is mentioned in the chapter, nothing (to me) suggests that "Sharkey" is supposed to refer to Saruman. It's almost as if the author meant to have Merry drop that comment after Saruman had made himself known, which happens just after Merry refers to him having caused all the mayhem in their hometown.

Unless I'm mistaken, when Saruman speaks at the door, it's supposed to be the "last big plot twist", with only clues suggesting that it might be Saruman, but nothing has been established... except for Merry the "spoiler hobbit" inexplicably saying it right before.

I've probably just missed something again. I seem to be easily confused as I've had quite a few instances while reading this trilogy where things didn't seem to make sense before somebody else explained it to me.

Answer 1

Merry was responding to Frodo, so immediately before your quote, there is:

'Yes, this is Mordor,' said Frodo. 'Just one of its works. Saruman was doing its work all the time, even when he thought he was working for himself. And the same with those that Saruman tricked, like Lotho.'

The chapter discusses Lotho, who made the money to buy up property by selling provisions and pipeweed to Saruman.

In addition, Bill Ferny was posited as an informer working with the other unsavory types in Bree in the first book. In this chapter, the "ruffians" are directly linked to Saruman:

[...] they were disturbed to see half a dozen large ill-favoured Men lounging against the inn-wall; they were squint-eyed and sallow-faced.

'Like that friend of Bill Ferny's at Bree,' said Sam.

'Like many that I saw at Isengard,' muttered Merry.

So they were generally disposed to blame Saruman for creating the conditions for what was happening in the Shire. It wasn't until Saruman shows up that they realize that Saruman is Sharkey.