I think that the whole point of italki is having native speakers correcting you, that is to say people you would never be able to reach out to otherwise. Even though corrections done by native speakers might not always be great, they're grammatically accurate most of the time, which is not the case for non-native speakers. For instance, in my language (french), I have very often seen wrong corrections done by non-native speakers who claim to have a C2 level.

I don't mind being corrected twice by two different native speakers because one of them will probably formulate things in a better or just different way. Still, both corrections are valid.

I think it's more of a problem when you get corrected twice because the first correction done by a non-native speaker wasn't right.

My point is that people are here to learn a language so they should be helped in the best way possible. I understand that it is fun and gratifying to correct someone else in a language that you studied yourself, but you also have to accept that there are probably more qualified people than you to do that on this site. You're not really helping people if you mislead them, even unintentionally.