> Do those ratings reflect actual tested durability or mainly marketing?

They reflect what the manufacturers will offer the warranty until. A quick google search suggests about 2 petabytes of writes is the max you can get on a samsung 850 before it completely fails (and after 1 petabyte you will have many failed sectors and data corruption starts creeping in)

At the same time, I bought my S3710 used and when I got it, it had almost 8 petabytes written and it's still just like new.

> Have there not been some relatively large providers using consumer SSDs in the datacenter successfully for some time?

Yes, that wouldn't surprise me at all. Like I said, for many workloads, consumer SSDs are acceptable. But that doesn't mean enterprise drives are a scam.

I noticed that the Samsung 960s are rated at almost exactly 0.3 DWPD, which happens to be the standard endurance for "read-optimized" SSDs, even across different generations of flash. This looks more like market segmentation than a measurement.