Rarity: It’s all about supply and demand. The rare what you want is, the fewer chances there will be to buy it. If other people want it too, then it can easily lead to a bidding battle.

All Greek Gold is rare by the standards of almost any other collectible.

Age: Not everything that is old is valuable and not everything that is valuable is old. However, if something is worth collecting, the older an object or picture is the rarer it is likely to be, simply because other examples of it will have been lost or broken over the years.
All Greek Gold is older than almost any other collectible.'    
http://www.gold-stater.com/images/greek/IMG_0084AlexMS.JPG Condition: Again, rarity comes into play. The rare an object, the less condition will usually matter, because there are comparatively few opportunities to acquire an example of it. Having said that, severe damage may destroy any value at all. In general terms, the closer an object is to its original condition, the better. Dealers like to buy unrestored items so that they can have them restored and realize the additional value. And there is a premium for modern collectables such as die-cast toys if they retain their original packaging in mint condition.

Provenance: This is the history of the object and who has owned it. The clearer this is, the better, and an association with a famous name or celebrated event can add significant value. In some cases, such associations can give otherwise everyday objects of no real value huge cachet, resulting in high prices at auction. By the same token, a lack of provenance or questions over the history of an object can cause problems, especially if there are concerns that an object might have been forged, faked or stolen.

Provenanced Greek Gold certainly commands a premium from advanced collectors.  

Names: Sought-after designers, clockmakers and jewellers, as well as others, can add huge value, so checking to see if an object has been signed or market is essential. Learn your terminology, though. Circle of…, Studio of…, After… or Attributed to… do not necessarily mean that they are by the artist/designer/maker in question.

Historical Names such as Alexander the Great, Ptolemy, Kroisos (Croesus), Darius, Euainatos, Kimon, etc, are always in high demand.

Fashion: What people like changes with the times. Victorian art and furniture, once the mainstay of many an auction, often get barely a look-in these days, while previously ignored areas like post-War design and Vintage fashion have become highly sought after.

Ancient Greece is always in fashion amongst the educated of the world.