Thanks, will have a look at tabulator. I appreciate a list of validators you published on FD site, can help at least a bit when working with non-techies to vet their data before submission.
Not on the list is ETLyte (https://sorrell.github.io/etlyte/), which I built so that an insurance company's corporate clients could vet their flatfiles before submitting them - it has worked very well across multiple files, with custom validations, and is very speedy (uses SQLite). As far as "non-techies" go, it's pretty straightforward, but confined to the command line, so I guess I need to get working on a web frontend for this :)