Considering a used 2020 Prius Prime - is this amount of rust OK?

Pretty sure every four year old car in the entire province looks like that.

 

Cars in Florida don't look like that

 

Depends on your tolerance. I’m on the west coast, relatively mild winters, but still zealous applications of road salt. Slushy salt might actually be worse?

anyway, about 4 years of ownership in, I saw the rust-bloom starting, didn’t like it. Opted to raise one end at a time, remove plastic panels, brush off loose rust and brush on boiled linseed oil. That’s worked well, with ongoing vigilance and a few touch ups.

But yeah it’s a little over the top. I don’t think today’s cars are protected as well? Never saw this level of rust with our string of Hondas, in previous decades.

nowadays, my wife and I both retired, when we do get snow and/or sub-zero centigrade temps, we’ve got the luxury to wait it out, and its garage stored.

But street or parkade parked in Montreal, with a 5 day a week driving commute, that’s tough on a car.

 

Yeah I didn’t get zealous on rust removal. Someone here recommended boiled linseed oil; I gave it a try, and it found seals well, lasts too.

Last pic here gives some idea:

Do you need underbody rust protection on new Prime? | Page 3 | PriusChat

 

Look into the "certification" programme that Toyota uses and make sure that it's a real OEM Certified Used Car, rather than some 'coverage' that merely certifies that it's a used car.
What kind of warranty and what is covered?

Frankly, I live in a more or less habitable part of the globe.
More, because cars only rust if they are imported from frozen wastelands above I-20 here in the US.
Less, because our humidity and temperatures are usually tied in a race for triple digits.

Our cars mildew rather than rust - but I am a little curious about a 'certification' process that fails to take note of what I consider to be a lot of rust. I would ask the dealership some frank questions about this and get detailed info about coverages for things like exhaust components and other underpinnings.

Then?
Take a look at some numbers and decide.

Rust is like the cancer that it is often compared with.
Just parking your car in a garage isn't going to mitigate this, and unless you invent a time machine(*) you are unlikely to make it go away completely.
Consider the time and effort required to treat the rust that's already eating away at your car against its cost. You will need to also need to estimate how long you need the car to remain economical to operate and compare this with a mechanic's estimation of it's life expectancy.

A mechanic that doesn't work for the dealership.

Oh - and if you DO invent a time machine, I'd shove a few cats through it FIRST.....just to make sure it works, and if you go back, buy some Bitcoin.
This way you will be able to afford a new car -

 

I'm a big fan of Phosphoric Acid, it turns rust into a black substance that arrests further rusting. The POR products combine Phosphoric Acid and Epoxy paint to seal and protect the metal: this works great for ambient temperature parts....not so good for exhaust and other hot metals.