30% is the standard retail markup for many things

It most certainly is not standard in retail. Most retail stores have a margin of a couple percentage points. Walmart, for example, is ~3% net margin most years

Unless you’re trying to compare wholesale price to final consumer price. In which case I would say that’s a silly and pointless thing to compare, but even then it’s far smaller than 30% across retail and varies wildly based on the individual item being sold

A 30% cut is only really common in the tech sector where the underlying economics make it feasible