If gold plated, not gold through and through, the plate will eventually wear away and the chains will tarnish in those areas. If a brass like metal is underneath, the color when shiny is close to gold and it might be hard to tell the difference until tarnishing happens. There are several ways I have seen suggested for home testing but I cannot recommend any as being reliable.

Acid tests are done by two methods. In one case, a bit of the item is rubbed onto a small slate "test stone", rubbing hard enough to remove some metal from the surface of the item. Gold of a know karat is also rubbed on the stone. Acid is placed on the marks and observed. If the sample dissolves right away, it is not gold. If the sample remains, the color is compared to that of the acid effects on the known samples and from that an approximate karat value is assigned. The test is better at telling what is not gold than closely telling the karat of the gold.

The other method is to make a mark on the jewelry in a place that shows very little. The mark must go through the surface and a bit into the metal. Acid is applied. If not gold, the metal is generally a base metal containing copper and the acid will bubble with a green color. This is a sure giveaway the item is not gold through and through. If the item is gold, the test may leave a darkened, tarnished looking spot or a dull spot on the metal. This can be polished and brought back to a shiny surface.

The jeweler may be incorrect is saying the chains are too light in color and too shiny to be gold. Gold can be as shiny or dull as the factory wants to make it. Color depends on the karat of the gold, with some color variations in the same karat of gold depending on the actual recipe used to make the gold suitable for jewelry.

What the jeweler may be referring to is the "look" of the typical heavy chain, stamped 14k with no makers mark, gold plated and not solid gold. We see these ever so often. These chains have a faky look, shiny but not well finished. I have seen so many those fakes are fairly easy to spot but a test is really needed to be certain.

As for prices, I hesitate to quote a price based on weight only. Too many other factors play, such as quality of the item in the first place. Quality varies from very fine manufacture to really cheaply produced items, made to sell at lower prices.

Look for a makers mark on the items you have. To meet federal law, the karat stamp should be there along with the makers mark. The karat stamp alone with no makers mark is clue to dishonesty. The mark is required to hold the maker responsible for the karat stamp being true and accurate. A karat stamp does not have to be put on an item but if it is, the makers mark is required by law.