There is a stain I had not seen.
'Macchia' — MAK-kya. Double 'c' gives a hard stop before the 'kya' sound.
Use when you discover a defect at home that was not visible in the shop. The pluperfect 'non avevo visto' establishes that you could not have noticed it before purchase.
'Avevo visto' is the trapassato prossimo (pluperfect) of 'vedere'. The negative 'non' with the pluperfect implies the defect pre-dated your purchase. 'Macchia' covers any mark, stain, or spot. This construction politely implies the shop is responsible.
Ha un difetto che non si vede subito.
It has a defect that is not immediately visible.
Diplomatic phrasing.
L'ho notato solo a casa.
I only noticed it at home.
Simple and clear.
Era nascosto dalla piega.
It was hidden by the fold.
Explains why you missed it in the shop.
Items sold 'as seen' at markets or during sample sales ('vendite campionario') may be explicitly sold with known defects. In those cases, return rights are reduced or waived.