Discount vs Surcharge – Nudging more sales [closed]

When creating a website I was asked a question on how best to display prices.

So I was asked "are users more likely to buy more if they are given a discount, or buy more if there is a surcharge on single items?

do you charge a surcharge for buying less? or do you give a discount for buying more?

the prices are the same, the framing is different, what do you guys think would nudge people to buy more?