Lead Fargoth outside and speak with him discreetly. The intent was to time it right before the smugglers would get into a... situation with the guards by the tradehouse. Presumably the guardsman presence has been increased as well, right?
"I've got some bad news for you. I was in the tradehouse and I overheard one of them, Hrisskar I believe they called him. It took me a bit to piece together what they were talking about, but they're gonna step up the shakedowns, and I think they're gonna start with you. They've decided you're holding out on them, mentioned you by name. So they think you've got a stash of some kind where you've been putting your gold."
Marcius gets a grave look on his face and puts his hand on the elf's shoulder.
"Fargoth, they're gonna pin a smuggling charge on you. And they're gonna take you for everything you're worth. You have to get out of Seyda Neen as soon as possible for your own safety. And if you have savings, anything you managed to save from these goons, we'll have to get that too. Can't leave anything for them to find."
Deceive this probably completely innocent individual. If it works:
"Okay, so we'll need to split up. I don't think the town's safe for you to be in for much longer. You'll have to get whatever you need for a trip. But you have to be careful - if they catch you carrying anything valuable, they'll confiscate it if they catch you. Then they can take it via civil forfeiture, so it's legally theirs."
"But they won't be looking for me, so I can slip out unnoticed, or at least without being stopped. You get out as soon as possible in the meantime - we'll meet up at this cave outside of town," Marcius says and gives the directions to Addamasartus. "I'll be there as soon as I can - I'll probably get there before you, so once you're there go in and call for me, I'll find you and we'll go from there."
"Good luck, and if they manage to get you, remember - don't tell them shit. They won't be able to beat the location of the stash out of you once I've moved it, and you're in the clear otherwise - persevere and they'll have to let you go eventually. If that happens, find me in Suran. I'll be near the harbor, I've got a friend there with a silt strider that can take us anywhere in Vvardenfell."
Hopefully I can get my hands on the stash, and whether a suspiciously quickly moving Fargoth is caught by the increased guard presence or not, the plan will go on!