If you ask someone what typical Czech products are, you would most probably get answers like crystal glass, garnet jewelry, wooden puppets or beer. These products are associated with Czechia because of the best quality thereof being produced there. Czech beer is the best in the world (Irish may argue, though) simply because the best hops and barley grow in Czechia and because of the six hundred years long industry tradition. Bohemia crystal glass is the best in the world because of the best lead-rich raw sand being mined in Czechia and because of the three hundred years long industry tradition. Garnet jewelry is the Czech original as this semi-precious stone is found in large quantities only in Czechia and nowhere else in the world.
But, what are the typical souvenirs, then? Souvenir is not the same as typical product. Souvenir is something you want to remind you of the place where you have been or would like to go to. Souvenir is something you want to wear like sweatshirt with some Czechia-related picture or text, something you want to display on your mantelpiece like miniature model of a building, something you want to see each time you open the door of your fridge.
Then you need to distinguish between souvenirs designed and made or at least elaborated in Czechia and those designed by foreign companies and made in China or other low-cost countries. The latter make no sense to buy, obviously.
So the "real Czech" souvenir is a T-shirt woven and sewn in Asia and printed in Czechia with a pitcure or text designed in Czechia. It is a fridge magnet designed and manufactured in Czechia. It is a miniature model designed by Czech artist and manufactured by Czech ceramics works.
How do you distinguish between authentic original and imported crap? Originals are more accurate, they model the reality with higher fidelity, use better materials, have sharper contures and brighter colors, do not show signs of copy-paste approach, and cost more.
Originals are for those who care.