What's the "shop level" for expedition vendors?

In the patch notes for 0.1.1 the "shop level" for expedition vendors is mentioned. Has anybody got an idea what that is and how in can be leveled up?

It levels as your character levels.

Right after finishing the Acts, all items sold by expedition members are item lvl 60. When we use the token to reroll the shop list, it refreshes the list and item lvl will be raised as the character levels then (currently) capped at ilvl 78 (listed items can be ilvl77 or 78).

At least this is what i've seen so far.

I see. Thanks.

I was thinking that maybe the "abilities" of the vendors would change with the "shop level". This would actually be fun, if the actual vendors could become better instead of just the items. Probably a missed opportunity here to inject more variance into the game and spice up events/rewards.

So it's nothing more than a seller basically. They also sell better items according to your leveling.