I ordered the same product (just different colors) domestically and overseas. The product was shipped via air from overseas. Domestic shipping was limited to ground only because of flammability risks. Overseas was subject to a 12 hour flight; domestic would have been, let's say, 4 hours. Not sure it matters, but the product was small sets of art alcohol brush markers.

Does it make sense and is it reasonable to limit shipping to ground domestically? Why can it fly from overseas but be limited to ground only here? What's the real risk of a fire from these markers?

Is the over-seas shipper properly declaring the contents?

Is the domestic shipper overly cautious with declaring the contents?

There's plenty of regulations for shipping by air when it comes to potentially hazardous materials like batteries and flammable material.

More regulations means more costs to keep up with those changing regulations. The domestic supplier may have just decided to avoid the costs of keeping up with air shipping regulations and the actual costs of air shipping.

Meanwhile, the overseas supplier presumably have their customers all over the world and shipping by sea is cost and time consuming if you don't buy full shipping containers. So they're already geared for shipping by air.