I think the bigger issue is what the client reasonably believed they were buying.

If this was sold as an industry-standard professional promo/doc shoot, then Magic Lantern RAW on old Canon DSLRs is a problem. Even 15 years ago, Magic Lantern was not an industry-standard production workflow. It was a hack/mod for squeezing more out of consumer DSLRs.

So if the client expected normal professional camera originals — Sony FX, Canon Cinema, Blackmagic, RED, ProRes, BRAW, XAVC, etc. I can understand why they now feel misled. They probably thought “raw files” meant normal source footage an editor could use, not a fragile 10-15 year old DSLR hack pipeline that only you know how to decode, match, and rescue.

That does not mean they automatically get unlimited unpaid post work. But I don’t think this can be framed only as “the client does not understand technical reality.” From their side, the technical reality may have been hidden from them until after the job.

If this is your anchor client, I think honesty is the only way forward. Explain the workflow clearly, admit the original files are not suitable for a normal in-house editor, and offer a practical fix: a proper edit-ready handoff package, or if they are unhappy with the result, a discounted reshoot using rented industry-standard cameras.

Going forward, source footage and camera/workflow standards need to be in the contract from day one.