Making a Shop

I need to know what a unit requires for it to function like a shop for (example Goblin Lab).

Also is it possible to buy items without the shop having the select unit/hero ability.
If it is not possible, Id like to know how to conceal this ability and allow players to buy from this shop without seeing that floating pointer above the units head.

Probably you could hide the select hero ability in a disabled spellbook.

You can edit the art of the Art - Target field of the Select Hero ability so that it doesn't show the arrow or if you only want that shop to not show the arrow, create a copy of the ability, remove the arrow and give the shop the new ability.

For acting like a shop, just give it the same abilities as one of the existing shops (Goblin Merchant for example has: Select Hero, Invulnerability, Shop Purchase Item).