I have the last say on recruitment for sensitive positions or management positions in companies we own. I look for honesty, not sugar-coated reasons for leaving/wanting to leave their current employer-companies.
But "of course", it's taken for granted, IMO: people move looking for greener pastures/career advancement -- otherwise , why will you move (unless you got fired/frozen??). So, I want to know the real WHY you need to move to advance your career or income.
IMO, no employer/company is perfect; it is just a matter of getting the current Best Fit between employer & employee. What may have been a Good Fit before no longer works now for either the employer/employee -- so, time to Change.
Thus, saying The Truth about an employer is not really backstabbing, it's just the plain truth.
Some Truths I have heard that are not backstabbing, IMO:
Insufficient/unfair compensation (be ready with your figures);
Company policy to favorably misrepresent itself to get more recruits in;
Almost impossible upward advance due to policy of putting in extended family members in top/critical positions;
Glass ceiling for female employees;
Position requires fabrication of documents/figures for government reporting requirements;
Supervisor (not company owner) makes personal demands (pick up kids, collect rentals , etc);
Current company not stable (there are times salaries are delayed, company has zero business, etc);
Our company is bigger than their current company.
As for a relocation working against an employee's commute time & expense, yes - understandable. I myself do not hire anyone who needs over an hour's commute 1 way. I have observed these employees with long commutes often arrive late, and tend to stop work & tidy up by 5:45.

.
IMO, The Truth always works in an applicant's favor. Sugar coating & run-of-the-mill buzz words/phrases are red flags to me: this applicant is not being truthful. Better I can assess more accurately your strengths & weaknesses -- after all, nobody is perfect. But there is always a good fit (but if there are money/equipment/trust issues underlying an applicant's exit from the previous company: then it's a no-hire).