Playing legit ranked games with friends - is there a rule against this?

This might sound silly but I thought I'd ask, because I guess you could elo boost yourself by playing ranked matches vs opponents who lose on purpose?

My friend and I play a lot of games (evident on my profile) and these are unranked casual games. He wants to play ranked games against me, but with my overwhelming win rate vs him, I'm worried this might be misconstrued as elo boosting maybe?

I also don't want my elo to go up artificially, I'm pretty dead set 800 elo range, and the last thing I need are stronger opponents...

How does it work out when you play a lot of games vs friends in ranked? Sometimes I'll try new ideas vs him, and won't punish his mistakes but let him know and continue the game that way.