The site said their products were new, but the keyboard I actually received had some marks on it, so I think it was used.
この場合、次のような言い方ができますよ。
ーThe site said their products were new, but the keyboard I actually received had some marks on it, so I think it was used.
「サイトには商品は新品だと書いてあったのに、実際に届いたキーボードはいくつか跡があって中古品だと思う」
ご参考まで！
Although it said it was new, the item I received had signs of being used.
ご質問ありがとうございます。
・「Although it said it was new, the item I received had signs of being used.」
（意味) 新品と書いてあったけど実際届いた商品は中古品の形跡がありました。
<例文>Although it said it was new, the item I received had signs of being used so I returned it.
<訳>新品と書いてあったけど実際届いた商品は中古品の形跡があったので返品しました。
参考になれば幸いです。
カナダ 
アメリカ合衆国 
