I have taken only a handful of guided tours over the years - never an individualized tour. I have no objections whatsoever to making a living as a guide. Generally, I've enjoyed learning about something new through someone else's eyes.
But IMHO, a concentration camp is a completely different situation. What history are visitors actually "thirsty" for at Dachau KZ? It's basically an intense review of public-school and Hollywood material that we've already fully absorbed. Do we want more previously-unheard, grisly details? I hope not. Do we expect new revelations about the Holocaust? I did not... that's completely unrealistic of course - but nonetheless, I did tour the place. Was I thinking my visit would help someone else, in some way? No. So then... why did I go?? No doubt I was just blindly ticking off the "must-sees" in my guidebook - which is probably what most of us do - without truly thinking about it. This was lazy, flawed trip planning on my part, pure and simple. All I got out of my visit was several hours of deep depression, which did nothing for me or anyone else. It was a wasted day, and I should not have gone.
Back now to guides... I cannot grasp the concept of sharing all that gruesomeness with a stranger, knowledgeable or otherwise. The facility itself will provide all the beyond-gruesome details you can handle. A visit to Dachau IME is much more a personal and highly emotional experience than an educational one. If you have personal or family ties to individual victims - my condolences in this case, perhaps it's a must see - I don't know. Otherwise, I'd suggest skipping it unless you just want to test your own range of emotions.