Was called in by a manufacturer re a warranty claim last week, oily spots appearing on carpet.
Allegedly marks had appeared on their own, worsening over time. This problem was also apparent in the back room, but I noticed the start of it in the front room!!
Sure enough, felt oily, but I wasn’t convinced it was oil. A quick test with water showed me it was water-soluble – can’t be oil!
The moisture meter went off the scale, indicating hygroscopic substance – detergents!
Asked the question and sure enough – she’d spot cleaned, using Preen DO NOT USE!
Testing less obvious spots in the front room – the same result! It looked different due to different fibre content.
So not a carpet issue, a maintenance issue. It has since been booked in to fix and been resolved.