Warranty terms, language support, needing a legal representative in every country, to start.

I'm a 1000% sure the place I order my stuff from in Germany doesn't have a representative in Finland.

That's the whole damn point of the EU.

I think there might be some regulation on having the instructions written in the native language, but that's like 100€ to a translator for an one-time job. No laptop comes with an extensive manual.

Warranty terms are EU-wide too mostly, there are some country-specific exceptions, but nothing that would require a huge legal team to handle.

Yeah that's what I thought, I've ordered from many places in the EU that do not have any kind of presence or representative in my country.

From Poland: obligatory non-renunciable 24-month warranty of fitness for the intended purpose for consumers. Instructions required in Polish. Detailed information about qualities of goods sold is compulsory (e.g. specification of components for a computer, just model number is not enough).

From Germany: specific requirements for "impressum" on each website. Definition of all quantities in SI units.

Things get more funny if you touch any food: labelling regulations have a common EU base, but definition of what detail level is required for each element is per country, and they do differ significantly.

For everywhere: obligation to collect and report VAT for each destination country.