Limit of exchening reviews

Hello guys.
I’ve stopped exchanging reviews after I got 100 5* with 500 downloads. Now I have 1300 downloads but reviews, of course, don’t grow up so much.

Do you think exchaning 5* is safe if you get so many of it?
Do you think it’s worth to do it in order to boost app position in google rankings?
Do you think it.s better to ask for 5* or 4* maybe to make it looks more natural?

I was just about to ask how is the general experience with this? I’ve noticed some sharp drops in downloads (from 1.300/day to 300/day for example) for few of my apps I’ve exchanged ratings for.

I’ve also mentioned, that a friend of mine got one of his apps suspended because of this.

I Google silently on witch hunt? I’m getting very careful with this stuff. Google is not stupid, after all.