If properly designed as "frost free" then it won't.
As i described above, such freezers typically have a finned heat exchanger (HE) with a fan that forces air flow through the HE and around the cabinet. Of course there will be condensation in the HE, and it will freeze - yer cannae defy the laws of physics.
But, if properly designed, the system will have a means of clearing that. In the case of my parents unit, it was a heater element embedded in the HE - so the controller could switch that one, warm up the HE, melt the frost, and it would then drain away. That could be a simplistic "every X hours, when fan and compressor aren't running, turn on heater for Y minutes", or it could be more subtle such as detecting when the compressor load changes, or the temperature of the HE goes lower than it should, and switching the heater on until the HE reaches a certain (above freezing) temperature.
Our current freezer has been running for something like 5 years without a defrost - so the system is working. My parents freezer would work fine for several years, then it would slowly degrade - my guess is that it failed to fully defrost, and over time the HE got more and more blocked, meaning that the ice gets more and more supercooled, and defrost becomes harder and harder.
This is a very different setup to the cheap (not frost free) system where there tends to be just evaporator pipes in contact with the freezer walls, or as a panel in the back, and which can never get above freezing without unloading the freezer and turning it off until it warms up.
Fine print will not get them out of that sort of thing. If a headline feature is "Frost free, forever" then that's what any reasonable consumer would expect. Courts take a dim view of "feature*" where "*" is defined in print too small for a gnat to read at the bottom of the advert or flyer.
