What should i do?

So i recently sold a north face hoodie on vinted and listed it as new without tags. I got the jumper a couple years ago, thinking it would fit me , however when i got home i realised the jumper was too small , and the shop was a couple hours away from me so i never bothered to return it. Anyway i decided to sell it as it’s been sat in the back of my cupboard for probably about 3 years now , and sold it to someone for £7. However, when i was about to package it, i realised there was a small red stain on the back of the jumper. I have no idea how this got here as i have never worn the jumper and as i said it’s just been sat at the back of the cupboard. I have washed it and am hoping the stain will come out, and i will tell the buyer all of this and asks if he would still like me to send the hoodie. Is there anything i can do to avoid a 1 star review if i have to cancel the sale? i’m annoyed as i feel like this is an honest mistake as the stain is so small it’s not very noticeable in pictures and i never noticed it beforehand because it’s hard to see on a black hoodie :( i would include photos however it’s difficult to see currently as i have just washed it and it is drying.