Sorry Distrubing you! I Had A Question For All Steemit User, Especially To Top User. BUYING UPVOTE ISSUES

MY QUESTION IS BUYING UPVOTE IS LEGAL OR NOT??
I NOTICED THAT WHEN SOMEONE BUY UPVOTE FROM BIG BOT, THEY WERE GETTING DOWN-VOTE FROM Hive account@grumpycat
SO WHATS IS GOING ON.BUY UPVOTE LEGAL OR NOT??
IF LEGAL THEN WHY grumpycat DOWN-VOTE THOSE POST.AND
ISN'T LEGAL THEN WHY BOT SELLING UPVOTE.

ANY STEEMIT RULES FOR UPVOTING???

PLEASE ANSWER ME.......

i know my english isnot good.