Oh, sorry, missed that in your OP but now I get it.
Oh, well, jadeite and nephrite are both real jade, and easy to tell apart with a bit of experience, so no worries there. Jadeite, which when high in quality is by far the more valuable, is glassy in shine, and the most typical valuable types are a brilliant, extremely glassy, semi-translucent to translucent apple green resembling emerald. Nephrite is waxy and never as translucent, and when green, is a dark, dull green. The glassy-waxy and translucency distinctions are quite dramatic. The green colors also differ markedly in quality. Of course, both come in many colors, but for expensive jadeite, green, or green mixed with white , is typical. For nice nephrite, jewelry is usually very dark green, but for carvings, a creamy, fatty looking white is highly prized too.
They might sell both, but should be able to tell you which is which. If they know their stock, they won’t try to fool you. Nephrite, being marginally softer (although very hard), is sometimes referred to as ruan3yu4, soft jade, or Taiwan jade (although much of the “Taiwan” jade comes from Canada). If made into jewelry it is typically a very dark, waxy green. Jadeite, being marginally harder, is called ying4yu4, hard jade, and often comes from Burma.
If you see bright, single gems at the government store they are likely to be jadeite; if you see darkish green pearl-necklace-style necklaces, they are likely to be nephrite. This is a simple function of mass and value; the necklaces would be too expensive if they were made of that mass of top quality jadeite. Simple bands of jade as rings, like a wedding band, smooth and without any carvings, are more likely to be jadeite at a jewelry store or government outlet for the same reason, although at the jade market they might be nephrite or glass.
Occlusions and so on also greatly influence the cost of jade. You can get real jadeite with good color but mediocre translucency and a few obvious occlusions for fairly low prices at the jade market. Perfection raises prices exponentially.
BTW, high-quality jadeite is worth a LOT. We’re talking obscene.
High quality nephrite in large pieces is still of very significant value.
Low quality jadeite and moderate-quality nephrite in large pieces, or high-quality nephrite in small pieces, are of moderate value.
Moderate to low quality nephrite is of little value, like the various stones that often pass for it. And if a seller tries to market quartz and similar stones to you as “yu4”, don’t punch them. The Mandarin concept is very vague, and includes a variety of similar stones. The sellers are not necessarily being dishonest – they might just be using the vague concept. The buyer is expected to be discerning. IMHO.
If you have any more questions please don’t hesitate to ask.