Extended sizing in golf apparel is uneven. Knowing where brands actually grade well saves a great deal of returning.
Plus size golf apparel has improved, but the range is still thinner than in ordinary sportswear and the quality of the grading varies more. Two brands offering the same size can mean very different things by it.
This is the distinction that matters most and it is almost never stated on a product page.
A properly graded extended size is re-patterned: the shoulder, armhole and rise are adjusted along with the width. A scaled one takes the standard pattern and enlarges it proportionally, which makes the armhole too deep and the shoulder too wide while the length grows unnecessarily.
You can spot the difference in the size chart. If the extended sizes continue the same increments as the standard range with no change in the length or shoulder figures, it is likely scaled. If those figures shift, someone re-patterned it.
Three places, in order of frequency:
Measure a garment you own that fits well and compare it to the brand's garment chart, not their body chart. That comparison is the single most reliable thing you can do, and it matters more in extended sizes because the variation between brands is wider.