Amber is fossilized tree sap, color depends on the type of sap and where it came from.  Terms such as cherry, whiskey and butterscotch refer to the color of the amber.  The majority of amber comes from the Baltic Sea and is most seen in modern silver jewelry.  There are major deposits in the Dominican Republic, source of the rarest color, blue.  On occasion the sap trapped insects or plant material when it was viscous.  This is rare and brings high prices.  Now to the issues of buying on eBay.

First of all, most amber from China is reconstructed amber at best or, more commonly a plastic like resin at worst.  You must use your intelligence to see if there are numerous copies of the same item, this is especially true now of kwan yins in a sitting position.  If you buy this type then rest assured, you are buying a decorative item, not an antique and certainly not amber.  There are real pieces of carved Chinese or Asian amber, but they are rare and hard to find.  Most of the fake amber offered from Asian countries is red or cherry, butterscotch is another favorite.  In most cases, the carving is much more valuable than the intrinsic value of the item. 

Another thing, "belles" or mermaids are not traditional Chinese art forms.  You will see many modern or Western icons made in "amber" and listed as antique.  Additionally, most of the insects trapped in Asian amber are modern or plastic.  Scorpions in the numbers being sold were not trapped back then, if they were then they were lining up at the trees for the next gob of sap to come down and engulf them.

Amber from Baltic countries is more likely to be natural though there are examples of recontstructed amber.  This is amber that has been melted and cleaned then re cast into chunks or molds that are then treated as natural.  One indication is reflecive flakes in the amber, though this does occur naturally on occasion.

Amber was very popular during the Victorian period and there are many examples of necklaces available.  Most were made of amber, however with the advent of plastic, bakelite was often used to imitate it. 

Testing amber is difficult, there are traditional ways such as floating it in a heavy concentration of salt water, it should float, touching it with a hot needle, you should get the scent of pine, if it is bakelite or plastic you would get the smell of burning plastic.  Another old test is to rub it with a woolen cloth, if it is amber it will get a static electric charge and will attract scraps of paper.

Hope this helps you in making your choices on eBay.