How do you find out the build year of a used bike? I have heard that older inexpensive bikes were more solid but I also heard someone say they thought the Chinese were improving their methods and materials over time. It would be nice to see some hard evidence one way or the other.
Google, bike forums, and serial numbers.It's not that the building of bikes has changed much, it's the materials.Though the OP is looking for a cruiser, there was a heyday (late 80's to mid 90's) when the 10 speed was turned into a beefy off road 12 speed MTB, bikes from that era,
"Bridgestone, Fuji, Giant, TREK, Raleigh, Cannondale,..." all used suprisingly nice materials, and everybody was trying to out-do everyone else in quality for the price, not penny pinch and cut corners.Consider the older Raleigh stuff (the 1939-70 ) their axles and cups/cones were made with a hardening process that is no longer allowed by any country, but of course you know that means it was a superior outcome, the older(now illegal to make) axles are a grayish color, and harder than any drill bit or cutter I have.I own a Raleigh Twenty, it's the only folder I'd consider motorizing because of the strength of build, it has wrap around brazed tubes that are a thing of beauty.
When you're buying chinese, you are buying something with no sense of "extra care" or "another eye" it's all by someone elses specs, after that it's your problems.Think Harbor Freight, that's a wallyworld bike, I have some Harbor Freight stuff that works great, and a bunch that broke the first time I used it, some that never worked.
A fine example of what quality bike you have, get your micrometer and look at the thickness difference between a wallyworld wheel cup and a used one from an old mid quality bike.They all roll, but to some it's a hobby, to me it's a lifestyle (carfree) and I can't afford to buy something that's painted gaspipe not worth fixing.