Have you ever noticed what Lucan Valerius says here?

"I've got some coin coming in from my last shipment..."

Lucan runs a General Store that mostly consist of random misc items.

What type of "shipment" is he referring to?

I think I've gotten it figured out.

Lucan acts like any run of the mill merchant but he's extremely shook up about loosing the Golden claw?

If you talk to Camilla she'll mention that Lucan has always been secretive about it and never told her where it came from, only that he showed up one day with it.

After returning the Golden claw to Lucan he'll mention that it's "smaller" than he remembers it.

He will then thank the Dragonborn and the quest will end.

After returning sometime later you'll notice that he has a whopping 10,000 Septims in his inventory.

Where could he have possibly gotten so much coin?

You know what I think?

I think Lucan is running a Skooma/Balmore Blue operation from his shop.

The reason that the Golden claw is "smaller" than he remembers it is because he would shave it down and mix the shavings in with Skooma to make Premium Balmore Blue.

Lucan is actually apart of Arvel's Bandit group in Bleakfalls Barrow.

He acts as the Skooma/Balmore Blue dealer and makes shipments all throughout Skyrim.

Lucan tried to double cross Arvel one day over a huge Skooma/Balmore Blue deal but ended up having his Golden claw stolen by Arvel's group.

He then task the unknowing Dragonborn with getting the Golden claw back.

Well, that escalated quickly.

The reason he has 10,000 septims is if you have the speech perk Investor and invest in his shop a glitch happens where instead of giving him 500 more it gives him 10,000 more.
Also, is there any evidence why someone would put gold shaving in skooma? Has this happened in other instances?

With alittle imagination it actually makes sense, that's the scary part.