At least here in Norway, though similar in many other countries that I know, it's not entirely bogus.
Typically there are real costs involved with submitting a customs declaration, especially if it requires actual people looking at the invoice and filling out the customs declaration based on it. An order from JCLPCB or similar would typically fall in that category.
Then there's the duties. Either they hold the goods until you've paid, in which case they need storage space and bookkeeping, along with inspections from customs every so often. Or they just pay up front and bill you after the fact. In either case there are real costs involved.
That said they're certainly not a charity, and I do think they exploit a bit the fact that often the importer doesn't have much of a say or knowledge in picking the shipping company. Perhaps the seller only deals with UPS for example.
But I agree that the transparency regarding customs processing fees is very lacking. Obviously they don't have an incentive as long as customers don't see this as a differentiator.
For example DigiKey allows me to select[2] between DDP or CPT, which means I have to pay for importing the goods[3].
[1]: https://en.wikipedia.org/wiki/Incoterms#DDP_%E2%80%93_Delive...
[2]: https://www.digikey.no/en/help-support/delivery-information/...
[3]: https://en.wikipedia.org/wiki/Incoterms#Allocations_of_costs...
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.