They sometimes want to make several trips in a short time instead of waiting for the Shadow to be back at capacity.

So they just want Shadows?

No, they also do other magic stuff and want other elementals.

Any kinds? Do they know there have been elemental-stealing bandits about?

Yeah, they have a plan to protect themselves from the elemental-stealing bandits.

What is it? People who have elementals would like to know.

It involves having lots of elementals, which is why they're buying them.

People who have or hope to accumulate many would still like to know.

They're gonna live on the moon.

Couldn't the bandits follow them with their stolen elementals?

Yes but the bandits would have to suspect they were there, and who would suspect that? Most people don't even know it's possible. 

If it's a secret why are they telling them?

These people are clearly nice and upstanding and not bandits.

That's very kind of them to say. They will tell their mage friends there is a buyer.

Great.

Later that day someone comes by with a docilely following Glass and Stone and says she might want to trade the Stone for an Ice or a Water if they've got one.

They've got salt. 

She thought they also had elementals?

Yeah but they're trying to collect more of them, they're not trading.

Where are their elementals? They aren't mages.

The mages and elementals are hidden because of the bandits.

So they're just sort of hanging out with no visible defense of their ridiculous pile of salt.

The means by which they're defending their salt are not visible, that's correct.

Seems ill advised.

Some people might get hurt trying to steal the salt but the smart ones will wonder how they got the salt in the first place unmolested and conclude there's probably something to be wary of. Even if (or maybe especially because) they can't see it.