Not what you're looking for but I feel it needs to be said. I'm sorry if this is inappropriate or rude, It's just my experience take it or leave it.

You know, as a student who was bad mouthed by my supervisor behind my back and also by my faculty at the school, while they pretended that everything was more or less "well" leading to serious issues for me, just keep in mind theres more than 1 side to every story. In my experience, for all the time that social workers are trained to be "honest" and "deal with issues transparently with the person you are having the issue with directly before going to other people" I found that there is a whole lot of being 2 faced.

Not saying you're doing this, but I can see why a student would feel like they can't be honest about a placement - because likely they are being lied to left and right. Generally its very easy for toxic environments to develop and its hard to be an honest communicator. My very biased opinion would be this: If you're too burned out to be a field instructor, don't be one. Because I had a field instructor who flat out lied to me all semester long and I had a horrible experience dealing with the fallout of all the bad mouthing she gave me. Again, not saying you're doing this - but please don't.