Short answer: a home refrigerator, range, or freezer is not certified to a food-equipment sanitation standard, and the FDA Food Code lets your regulator reject equipment that is not. The residential unit is cheaper on day one and a liability the day the inspector walks in. Here is the exact rule, and why it matters even more when you buy used.
What the Food Code actually says
The 2022 FDA Food Code, §4-205.10, ties compliance to certification by an accredited program:
"FOOD EQUIPMENT that is certified or classified for sanitation in conformance to a recognized American National Standard by an American National Standards Institute (ANSI)-accredited certification program is deemed to comply with Parts 4-1 and 4-2 of this chapter."
NSF is the best-known ANSI-accredited certification program for food equipment, which is why the industry shorthand is "it must be NSF-listed." The Food Code does not merely gesture at certification either: elsewhere it names specific standards as mandatory, including NSF/ANSI 18 for food and beverage dispensing equipment. A residential appliance carries no such certification, so it never clears this bar.
Certification is about sanitation for a reason: commercial-listed equipment uses non-toxic, cleanable, corrosion-resistant materials with coved corners and smooth welds, sealed so food debris and bacteria cannot lodge in seams. A home fridge is not built or tested to that standard, no matter how cold it gets.
Why this bites hardest on the used market
The certification requirement does not care what you paid. It applies to a $200 auction find exactly as it applies to a new unit. The used-market trap is the plate: NSF certification is proven by a legible NSF mark, and on old equipment that plate is often painted over, corroded, or simply gone. An inspector who cannot read the certification can treat the unit as uncertified, and a bargain becomes a fixture you have to replace before you open.
So the pre-purchase check is not only "does it run." It is: is there a legible NSF/ANSI mark, and does the data plate match the machine? That single look separates a genuine commercial unit from a repainted lemon. It is the first item on the 20-minute inspection, and it is the reason a suspiciously cheap "commercial" listing at an equipment auction is worth a second look before you bid.
Before you buy any used cold-side unit, check the model against its documented failure modes and real repair-part prices: browse the model records.