A close photograph helps show the patch, but a wider view gives useful context. Mention peeling paint, loose seals, staining or earlier damage without testing or scraping the area. Tell us when you first noticed it, whether it has spread and what has already been applied. This information helps us arrange assessment and avoids treating every dark mark as the same job.
If you also want unaffected rooms cleaned, explain those tasks through a separate one-off home clean. General household cleaning and mould investigation have different purposes; agreeing one does not include the other.