JLCPCB recently started offering them as a shipping option, and they tend to be $5-10 under DHL's quote. The DHL price takes the additional processing fees into account and I'm not left with a nasty surprise in addition to the tariffs/customs fees.
There's the option of doing it yourself or have some third party doing it, though you usually still end up paying some fee to the express company.
A lot of business customers do that, at least here, especially if they got goods with duties where they might not be confident in the goods classification[1] done by the express company, or if they have exemptions.
Though as I mentioned earlier, I do agree there's too little transparency here, and that they're taking advantage of it. I suspect the only way they'll improve is if customers start voting with their wallet.
[1]: https://en.wikipedia.org/wiki/Harmonized_System#Classificati...
Export or import classification? The first six digits are the same, but the rest vary per country so if you specify the export tariff codes then the one doing the import declaration will still have to do the import classification.
Haven't had to classify when ordering from JLC, then again I've only ordered PCBs so that might be why.