Is it permissible to sell goods at their normal price to employees within the establishment without the owner's knowledge, and must I pay the grocery price or the normal price when purchasing for myself?

The agent is not permitted to sell for less than the price set by the owner of the merchandise, because his actions are restricted by the principal's permission. If the agent violates this, he has overstepped his bounds and is liable for the damage incurred by the principal, whether he sold to himself or to another.