A few years ago some granite countertop fabricator began offering a free sink as an incentive. Some hid the cost in the price of the countertop. But nearly all looked for cheaper sinks because if you are giving away a free sink then the most important thing about the sink is not the quality but the price of the sink.
Stainless sinks are required by the major model codes in the US and Canada to be certified by an independent agency to meet ASTM112.19.3. This is an expensive process that includes testing in the factory and aftermarket. A certified sink must be marked with the manufacturers name and the certifying agency. Most cheap sinks are not certified.
Sinks should be made of appliance grade 304 stainless steel so they match the appliances now and in the future. Many uncertified sink are made from unknown materials. It may look good out of the box but not match your appliances or hold up over time. Even some certified sinks are made from 301 stainless steel. 301 has less chromium so it will not be as lustrous and will not match appliances. 301 Stainless also has less nickel so it will age faster.
Most free sinks are double pressed so they are lighter which means they are will be noisier and do not resist denting.
Many free sinks are unbranded so there is no one to stand behind it if there is a problem.
If you install an uncertified sink and there is a problem it can only be replaced with a sink from the same manufacturer because the cut outs are manufacturer specific.
Here is a video except from a recent presentation we did for a customer.