Potentially boosted account - ELO boosting - Illegal or common practice?

So I had a chance to chat with this person in the invite after the game to play together, and this was before I knew about this user, I find it odd that this player is this good from an account that has a Platinum 2 status without a single previous ranked status. But this is what happened after the game when the game ended and I added this person.

The user mandaravå is asking in order to win games for you (He typed in Chinese), I would need to ask for a payment. So I am assuming this type of activity is illegal, with leveling up and asking for payment on this account. I am pretty this player mandaravå is boosted and asking me to pay for his/her services to boost up and winning games. I am not 100% sure if it is illegal or not, but I've been seeing this a lot based on my experience, and I'm wondering how is it possible for someone to ask for payments to get boosted? Or is this something that's common practice?

I already sent a ticket, but I want the communities opinion on this, is this a practice that you don't like, or simply players don't care as long as it gets to their objective?