Compare against the best, side by side, at the same size

Open your page and a reference you respect at the same viewport and zoom. Look for the gap in three places: spacing, type and alignment. Then try the squint test (blur your eyes: does the hierarchy hold?) and the 50% test (zoom out: do sections have a rhythm?).

Ask the agent to measure rather than guess: "list the font sizes, line-heights and spacing values on this page; flag values that are not on the scale."