Another point to consider- even if we were to consider this a case of Toeles, the CC clearly writes that one may not say the LH unless he first tries to be מוכיח the person. So in this case, if a eatery served you a subpar meal, we could only entertain spreading that fact after first speaking to the manager and telling him our concerns, and suggesting how he can improve.
Besides for being a תנאי in hilchos LH, it is also the mentschlach way to act to another yid. Why would we besmirch another yid and cause him potential agmas nefesh, if we can help him improve and be successful?