I am sorry to hear that. I have never personally been to Greenhills, but many people seem to have had a similar experience there. From what I have heard, all sellers claim to have South Sea pearls but sell Chinese freshwater.
The first set is clearly bead nucleated freshwater. It resembles a freeform baroque South Sea, but does not quite look the same. Here is a South Sea strand. You can see the similarity:
Those are akoya. Akoya have those clumps and protruding waves of nacre.
www.pearl-guide.com
Here are bead nucleated freshwater:
I just arrived today from a quick trip to Asia. I was finally able to examine a sizable lot of nucleated freshwater pearls. Although I am not sure yet of the marketability of nucleated freshwaters, I did buy 2 strands (not to sell, only to photograph, examine, and maybe send one to the GIA to...
www.pearl-guide.com
The earrings have the shape, the color, the luster, and the surface of freshwater pearls. If I only saw pictures of the rounds, I would lean freshwater but would not be certain. But the buttons are without question, as is the set. This tells me they are all freshwater.
I know that the set with silver and stones was composed of freshwater because of the pearls again, and because the design is a common one made by a company in Zhejiang and sold at most of the kiosks in Shanxiahu.
Yes, you probably could have purchased the pearls for less in China as this is where they came from. But not for $2 - based on the size of the pearls. You mention one pair as 15mm. If they are really 15mm, that is a huge size, and they should be set on gold, not silver. Large round freshwaters are not cheap.
South Sea pearls are in a totally different league when buying and selling wholesale. Because producers sell them at auction, you are not going to find a "special place" to get them cheaper than the other guy. The best possible price will always be right around yearly market value. And to get that good price you have to be willing and able to spend hundreds of thousands of dollars, and have a producer willing to sell to you. I am guessing you spent around $20-$40 for the earrings and around $100 for the set. That would be China pearl market approximate value (set on silver). If the pearls were South Sea, the set would have cost $2-$3000, and the earrings around a thousand per pair as well, even though they are commercial quality.
Because South Sea pearls are so valuable, a lot of people try to pass other types of pearls off as South Sea. We see this constantly on eBay - white freshwater pearls sold as South Sea, black freshwater sold as Tahitian. We also see it online.