Bolt stick is very common with the US made Tapco G2 FCG. If your bolt sticks when pulling it slowly to the rear doesn't mean it will stick open when firing. One of the problem that causes your bolt to lock open is the receiver to bolt guide fit is too tight which a little bit of light sanding will cure. Removing the FCG and running the bolt through it cycle will verify if there is enough clearance. Slightly canted sights can also be cured by re-aligning them. Don't let very minor problems discourage you from buying an AK, but instead use them as a bargaining chip to get a better deal. The things I would mainly look for is:
(1) the rivets being flush
(2) the receiver being square
(3) the bolt closes fully on a go gauge/live round
(4) examine the mag well to make sure it wasn't poorly grindded open
(5) excessive mag wobble.