Sometimes I notice the same users repeatedly making suggested edits, with some kind of general pattern of issues - they're generally fixing real problems, but also making erroneous changes of some kind in the process. I generally "improve" the suggested edit, and try to decide whether the helpfulness (finding a problem) or the unhelpfulness (messing things up) is more significant. And of course, sometimes they just have to be rejected outright.
As long as I'm putting in that effort, I'd like to be able to let these users know about the problems with their suggestions. I know that if I mark it as helpful, if they really wanted to, they could look at the edit history and see how I improved it. But that's unlikely to begin with, and the ones where it'd really be good for them to see that are the ones I did not mark as helpful. Is there anything I can do besides just trying to talk to them in chat, which feels uncomfortably like public shaming? Should I switch to rejecting the edits with custom comments? I'm hesitant to do that when I see that another reviewer has carelessly voted to approve a bad edit, or when the edit should really be improved and marked as helpful.