ballpark premium for corner unit + balcony

The premium can be any amount and it varies based on specifics. It's impossible for anyone to give you a good answer without more details. It really depends on the view, the layout of the apartment, the building, the condition of the apartment, the difference in monthly maintenance costs, etc. If anyone gives an answer without knowing any of these specifics, then they are just wildly guessing.

Thanks - if it helps, the apartments are in the same condition (newly renovated), very similar monthly maintenance costs. The view differs in that if you look down, you see the street corner. There's somewhat more light in the corner unit, but since it's a lower floor, the views don't change considerably (both still looking at buildings). The reason I ask is because the current asking premium seems quite high - the corner unit with decorative balcony is asking about 9-10% more. is this unusual or fairly standard?

if the additional exposure in the corner unit were to be nice 10% is justfiable but not from what you describe.