Nicholas is back for a second go around, having edited the previous version. Let’s see if we can help some more.
Finn is your viewpoint character. It’s important that his name be the first that is mentioned. Start with and introductory sentence showing Finn doing something interesting.
“I have a job for you.” Aost smoothed the parchment on the oak desk. “There is a merchant in town. You might know him. Mills?”
You can get rid of the first sentence. The fact that Aost has a job for Finn will become apparent through the scene. You can combine the remaining dialogue and make it a bit more concise: You know that merchant in town? Mills?
“That old fart? He still buy from us?” Finn’s amused gaze drifted from the window to Aost.
Did you mean “buys?” It’s okay to have him use incorrect grammar if he’s consistent.
“He does. When he can offer a good price.”
Delete “he does.”
“So what’s the job then boss?”
You can introduce a bit more conflict here to liven it up: What’s he got to do with me?
“Don’t call me boss. How long have we known each other?” Aost said.
“Fine, what’s the job then… my lord” Finn smirked as he fumbled with a quill.
I like the quip, btw. Why’s Finn fumbling with a quill? It’s also not clear to me where he is in relation to the desk and the window. Show him in front of the desk. You need to ground the reader in the scene with details. Describe the room. Give me something visual to latch onto.
Aost sighed and slid the parchment across the desk. “Sources retrieved this from a messenger. Give it a read.”
Resist the Urge to Explain (RUE). The action of sliding a document to someone implies that you want them to read it. That last sentence isn’t needed.
Finn grabbed the note. He squinted and turned the parchment, it said something about a big job tonight and getting back at those rotten thieves. Finn tossed the parchment down. “So Mills is planning something. What do you want me to do?”
It’s not clear here why he’s not able to understand exactly what the note is saying. You made progress here in showing, but it’s not quite clear yet. Make sure that your reader understands why Finn isn’t able to ascertain all the details from the note. Alternately, you can just show him grabbing it, squinting at it (we’ll assume he has bad eyesight), and tossing it back down. The part about what the note says isn’t really needed here. Instead, you can reveal that in the dialogue.
“He is asking around town for independent thieves to work on a job.”
Try contracting “he is.” It will sound less stilted.
“You want the guild to do the job?” Finn went back to staring out the window.
This could be clearer. What you’re trying to say, I think, is: You’d rather he use the guild instead of independent thieves? You don’t quite achieve that here.
“We are the job. Mills is planning to steal from the guild. He is asking thieves to rob our storehouses.”
Combine the second two sentences: He’s asking thieves to rob the guild’s storehouses. As you have it now, all three sentences say the same thing. Don’t repeat yourself.
“Our storehouses are hidden and well-guarded. Even if he did find thieves stupid enough, they wouldn’t make it past the traps.” He took pride in the traps he set for the guild.
I’d prefer that last sentence to be something like: Finn smiled as he thought about the traps he had set. Play with the wording, but show him being proud instead of telling us he’s proud.
“He offended Me. He offended the guild. He’s offended you.” Aost adjusted his sleeve cuff and reached for a quill. “Teach him a lesson.”
Would it be better if Aost were more emphatic here? Maybe have him start this speech with: Aost slammed his fist on the table.
The dusty red cushion of the window seat gave little support as Finn sat. “I’m not an assassin, Aost.”
“I’m not asking you to kill him.” A hint of irritation in his words.
This last isn’t a sentence. It needs to be something like: A hint of irritation tainted his words. As it is, you don’t have a verb.
“I’m asking you to rob Mills.” Aost scribbled something onto the parchment and folded it. “Show that coward that he can’t cross us. We are masters of our trade.” He slid the parchment into an envelope and picked up the burning candle, letting its crimson wax drip to form a seal. “Leave this for him when you’re done.” Extending the envelope to Finn.
This last still isn’t a sentence either. It needs to be: He extended the envelope to Finn.
Sighing heavily, Finn shuffled to the desk. “Any more details? or just rob the guy?” Grabbing the envelope.
Do you need “heavily?” I don’t think it adds a lot. Get rid of the question mark after “details.” Make that last phrase into a sentence.
“I’ve arranged for him to meet the fence at Mog’s Tavern tonight. He doesn’t think we know about his plan.”
“The fence” needs to be “a fence.” “The” implies that you’ve already mentioned a fence and refers the reader back to him.
Finn detected a tone of satisfaction. “Mog’s Tavern? I hate that place, drunks vomiting all over.” Finn held his nose. “So you want me to take his wagon?”
I don’t like the conversation here. That last sentence seems tacked on. Consider adding a sentence where Aost comments on the tavern to explain the “tone of satisfaction.”
“Do whatever you have to. Just get the job done.” Aost brushed away a lock of gray hair from his wrinkled forehead and reached for his cane. “Just remember to leave him that note. And don’t get caught!” he shot Finn a scowling look.
Delete the first sentence. Delete the second “just.” Capitalize “he.”
“Sure thing, boss. Go take your nap now.” Finn waved his hand as he left the office.
End the paragraph here.
The heavy oak door crept shut behind him. He tucked the note into the leather pouch at his hip and set off down the hall. The floor creaked under his boots. Aost had the nails pulled up slightly for this very purpose, it warns him if someone comes. A thief thwarts a thief, Finn thought; or was it the assassins he was afraid of?
You need to vary the sentence structure in this paragraph. Each one is subject – verb. Make one start with an introductory phrase. As it is, it sounds choppy. You need a period after “purpose.”
He stepped into the cobblestone street. They were alive with merchants and shoppers.
Combine these two sentences: He stepped onto a cobblestone street alive with merchants and shoppers.
Beggars nipping at their heels for a piece of coin.
To make this a sentence, “nipping” needs to be “nipped.” “Nipping” (the way you have it used) is a noun. “Nipped” is a verb.
The mid-afternoon sun filtered through the dense collection of buildings. Only a few hours of daylight left and things needed to be in place for tonight. Only, Finn didn’t know what those things were. Aost had provided him nothing.
You start two consecutive sentences with “only.”
Hope this helps!