This is purely opinion on my part, but the SKS was created in Russia, and made there for a number of years before the Chinese began manufacture. The Russian SKS tends to have better quality machining than the Chinese. Both are good, but the Russian is the original, and the better built rifle. Examine one of each side-by-side, and see what you think.
Markings.
Is it marked with Chinese characters or in the Cyrilic alphabet? <><><> As above. In addition, MOST Russian SKS rifles had blade style bayonets. MOST Chinese rifle had a spike type bayonet. But marlings are the defintive answer.
Value of ANY gun is based on exact make, model, and condition. A well worn Yugo SKS may be $150, while a pristine Russian SKS is $500. An average Chinese SKS is around $250-$275.
No. ALL SKS rifles - Soviet, Chinese, Albanian, Yugoslav, Chinese, Romanian, N. Korean, N. Vietnamese and East German - are chambered for the 7.62x39 M1943 cartridge, and can facilitate only that cartridge.
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Russian
they are about $100
Importer name
They began production of the Type 56 carbine (the Chinese designation for the SKS) in 1956, and production (for the civil market) continues to the present day.
20-45 USD
The RUSSIAN SKS may be date marked on top of the receiver cover (properly called the rear housing) , along with the symbol of the arsenal that made it.