7.62x39 rifles and their inherent accuracy depends on a very minor few things: whether the barrel is chrome lined or not, rifling condition, then barrel length (if it's too short), and whether there's a bipod on the end of your gun.
Any AK variant is going to have your typical 16" barrel length, unless you're talking about the AMD65, a krinkov variant, or a AK pistol. So this is of no worry to you.
Any AK variant is going to have your typical chrome lined barrel unless it's a "true" yugoslav variant, which doesn't have chrome lining because Chromium is as rare as hot women in their home country. A non-lined barrel is more accurate because it grabs the bullet better. It is also harder to clean and will wear out quicker over it's lifespan of use (if you actually shoot it, that is).
If you have a RPK, you need to check if it's a parts kit gun. If it is, it could have a blown out barrel. Also, if it's got a bipod, the harmonics of the barrel is going to be funky.
Poor riveting comes from bargain builds. Century is known for it (in the past), and recently Lancaster built AKs have had a very terrible reputation for rivet failure, or FTF. Stay away from Lancasters at the very least until they get their shit together.
Century Arms has kind of cleaned up their act. They may still put together one of the ugliest AKs on the face of the planet, but at least it's probably going to fire. Or you could vie for a Cugir, Romania built WASR instead of a cobbled together parts kit on a Cugir WASR receiver.
Poor magazine fitting is due to the nature of a WASR- their receivers have "magazine plates" that are welded into the receiver, unlike your "true to design" AK magazine dimples that are formed in the receiver. This really isn't an issue unless you're a purist or a snob. But you are buying an AK, so if you're acting like a snob, you're smoking something pretty good or have a few screws loose in your head.
If you wanted to go for a gun that actually will have a high resale value down the road, buy a Arsenal rifle and get it neutered. Their rifles only get more expensive as time goes on and their models get discontinued. It's more of an investment, and it's one of the finer AKs you can buy.
Or you could build your own or convert a Saiga, blah blah blah