Swirl marks are a physics problem: how desert dust scratches clearcoat
This is why the cheap wash is often the expensive one. A brush wash, a bucket wash with a single bucket, or a well-meaning building watchman with a dry rag will each install thousands of micro-scratches per session. Individually invisible, collectively they scatter light and make the paint look dull and grey. A proper wash in this climate follows a strict sequence: pre-rinse or snow-foam to float the grit off before anything touches the panel, then a lubricated wash mitt, then two buckets so the grit rinsed out of the mitt never returns to the paint.
Understanding this mechanism changes how you evaluate detailers. When you compare vendors, the questions that matter are not about the shine at handover — anything looks good freshly dressed — but about process: do they pre-rinse, do they use grit guards, do they dry with plush towels or a blower rather than a chamois dragged across the surface. A detailer who can explain their wash sequence usually gets the harder stuff right too.