It really depends on use. Unfortunately, I don't know whether there is an easy (and accurate) way to measure battery capacity at the time of sale.
I've been very hard on my Bolt EV, cycling the battery near 100% (from 100% to near 0% back to 100%) on numerous occasions. As far as I could tell, after 70,000 miles, I had 6% to 8% degradation, and in the last 18,000 miles since, it doesn't appear to have gotten significantly worse.
Some Bolt EV owners who have not been so hard on the battery appear to still have nearly 95% of original capacity, even over 100,000 miles.