Actually, 'rim' diameter has zero to do with the odometer being off. It's the tire size. More specfically rolling radius. You can actually put a smaller diameter tire on a 20" rim than what may have come stock on a car with 15" rims. Replacing stock 225/50R17's with 225/60R17's on the same 17" rims will make a 7% difference in the speedo/odo reading.
My new 245/45R18's are mathematically 3% larger than my stock 225/50R17's with 30K miles, but when I got them, they measured almost the same rolling radius. Likely due to having slightly less tread depth than the stockers. Tire pressure also makes a difference in rolling radius.
As discussed on previous threads, tires wear, so they're never the same diameter as the computer assumes they are. I think when we did the math last time, a new tire going bald looses ~2% of it's diameter due to worn tread. So 3% is in the noise.
Now my Jeep is another story. Putting 31" diameter tires on a Jeep that came stock with 28" really throws the speedometer (and odometer) off. Fortunately on that truck, changing speedo gears is very cheap and easy with plenty of tooth selections from the factory.
I agree with Koz, mileage is not a good indicator of the condition of a used car. My last jeep had 230K miles and ran and looked like one with only 30K miles. My sisters Corolla looked like a wreck within a year of her buying it.