Well they're two different Magpul Stocks.
The top one is a CTR model
The bottom one is the ACS model
Top one could fetch 50-80 (used)
Bottom about 80-100 (used)
Real thing would be worth more, fake one would be worth less. However, the fakes are nearly indistinguishable in Magpul when it comes to their airsoft stuff. I'm pretty sure the fake stuff comes from the same factory, lol.
Just take a peek there.