How to trigger vendors giving level-matched equipment in the Holodome and Claptrap, before Regolith Range?

Solution 1:

Yep, seems like it's hitting LV 8. It's happened twice at that now.

And LV 10 unlocks class mods and cryo spikes for Nina's Item Of The Day, and Cryo Grenades for Marcus's Bullets. Or the Cryo element in general...

LV 12 gets Nova and Maylay shields Unlocked... And Corrosive? And purple Oz Kits?

LV 13 unlocks Blue-rarity Class Mods as Items of the Day, and unlocks Booster Shields?