Online:All's Fair

Quick Walkthrough
# Search Bar-Neeus' tent and inform Sarisa Rothalen.
# (Optional) Talk to Bar-Neeus.
# Help Sarisa, or help Bar-Neeus.

Detailed Walkthrough
Talk to Sarisa Rothalen in the northern part of Riften.
:"The giant left us little more than our lives. We have no wares and no coin to rebuild. My mother is too proud to admit it, but this may be the end for us."
:Sounds grim. Can I help?
:''"Perhaps. I hear the merchant Bar-Neeus may be peddling illegal goods in the central market. If this could be proved, he'd be ruined and we would take his place."
:But how to prove it?
:"Go to the central market and search Bar-Neeus' tent. Look for anything he might be hiding. Report back to me with your findings."
:I'll look into it. (Starts Quest)
:"Some of the guards are willing to help us, but they need an excuse. If you search Bar-Neeus' stall, you might find illegal wares. My family would be in your debt."'
:Why single out Bar-Neeus?
:"We offer the same goods. By eliminating him, we claim a prime location and eliminate a direct competitor."

You have a choice: you can help the Rothalens and search the tent, or you can tell Bar-Neeus about Sarisa's plan.

Bar-Neeus' Stall
You need to search Bar-Neeus' tent, then report your findings to Sarisa Rothalen. 

You can choose to talk to Bar-Neeus. You can greet him three different ways. The first outright asks if he sells illegally imported goods, the second notes that he's stall looks untouched by the giant, or the third choice mentions the "rumors" about his stall. He denies that he sells illicit merchandise, and you suggest that you could come back after hours, ten he warns you to back off. He offers his help to his fellow merchants whose wares were damaged in the attack; all they need to do is ask. He thinks the rumors are simply coming from jealousy; it's tough to be a merchant in Riften after all.

You can search the chest as well, but all you find are ordinary supplies. Return to Sarisa. You didn't see anything illegal, but she is sure he is doing something illegal. You can tell her you're with her, or tell her you don't like where this is going. If you choose the second option, she says she thinks it is odd that Sinmur didn't even touch the stall. She suggests that he could be involved with the Worm Cult.

Her plan is to have you plant a flask of Altmer ale in his stall, then notify the guard. She offers to reward you well. You can tell Bar-Neeus about the plan, or carry it out.
Helping Bar-Neeus
If you choose to tell Bar-Neeus, he says she would rather lie and steal than ask for help. However, he gives you a package for her to extend his friendship to her. 

Return to Sarisa with the package. She says it holds supplies and gold— he has "shamed" her. She accepts his gift, but she definitely resents it. She gives you a reward.

Helping Sarisa
If you choose to help Sarisa and hide the Altmer flask of ale in Bar-Neeus's stall, you'll have to report him to the Constable Bronorr inside the Fighters Guild. 
:"Yeah? What is it?"
:'''You've heard of Bar-Neeus?
:"That Argonian? Aye. Never trusted him. Too friendly. Heard the rumors surrounding him, but there's never been any evidence to justify kicking him back into the river."
:I saw flasks of Altmer golden pear ale in his supply chest.
:"Troll's blood! Now we've got him. I'm gonna enjoy this!"
:I'll be right behind you.'''

Then you'll be directed to Bar-Neeus' stall where he will protest in vain about being arrested. You'll meet Sarisa a few steps away and she'll give you your reward.
:''"That's a shame, but he would have been caught one day or another.
:Glad I could've helped you. What about my reward?
:"Of course, gladly. And you have the enduring friendship of the Rothalen family. Let us never speak of this incident again."''
  

Quest Stages