海千山千, うみせんやません
May take 'no', yojijukugo
cunning and experienced in the ways of the world, crafty and worldly-wise, sly old (fox)
あいつは海千山千だから、取り引き相手としてはかなり手強いぞ。
だから
Conjunction, See ですから
1. so, therefore, accordingly, consequently, on those grounds, that is why, for that reason
Expression, at the start of a sentence
2. like I said, I told you already
1日中テニスをしていたのだから。