Ah yes, we have a lot of those stores in Prague. They're mostly just “tourist traps”. To understand weed in Czechia: Growing, possessing and distributing weed (that actually containes THC) is officially illegal in Czechia. read more
In the United States by far the largest convienence store chain is 7-Eleven. As of 2016 the chain opened it's 60,000th store. Wow! read more
THC is what makes marijuana from cannabis. THC level is regulated by law, and THC containing plants could be legally used only for medical purposes in Czech Republic, otherwise they are illegal (But it is apparently quite easy to buy real marijuana in black market in Prague). So products you saw in markets are not narcotic. read more