Do you mean based on the login to the POS by staff (i.e. the PIN number you use)? Or based on the customer entity you select? I believe if you are charging different prices based on who is purchasing the items, you would be using customer entities for that.
You can set a customer type (normal / supplier) using a custom field on the customer entity.
Add a ask question action with just question of TEST and OK button and put it in the rule after the change price list action.
That will give you a visible sign that the rule is firing.
If it shows the test message it means the rule is firing but something wrong further down the flow.
If it doesn’t show it tells you that problem is more likely your rule constraints.
Add the ask question and let know if the shows or not.