The management conducts the interview carelessly and half-heartedly. They just go through the motions, verbally agree to your conditions and urge you to resign from your current job first. After you’ve actually resigned and completely lost your bargaining power, they then start demanding to postpone your start date, and ask you to work for free / unpaid for a period of time. During this time, the company quietly continues headhunting-style recruitment in the market — keeping it very low-profile so the incoming employee won’t notice. Once they find someone willing to accept an even lower salary, they fire you during the probation period. The whole strategy is designed to squeeze the cost to the absolute minimum. Completely without honor / no regard for basic decency.