Using Auctions to Assess Prices
One of the better ways to determine current prices of cut glass is the various auction houses.  The prices paid by buyers at auction will provide an idea of what one might expect to receive for a particular item.
Dealers also attend auctions and they mark up prices in their shops or at shows in order to make a profit.
E-BAY may or may not be a good source to determine prices.  Prices on e-bay are often inflated as the buyer has no good method for determining condition, etc. before purchasing an item.
Shows and antique shops often have a wide range of prices for the same pieces. 
In the end, one must educate oneself by attending various shops, shows, and auctions in order to build up a knowledge of the various prices as they relate to such things as manufacturer, chips, cracks. repairs, etc.
Determining a Fair Price
In general, the older the piece, the more expensive.  This is assuming that the older the piece the more scarce it is.   This may or may not be true for a particular item.  One should not expect to pay a largely inflated price for age alone.
Nicks, cracks, and chips tend to lower the price.  Something that is mor than 100 years of age should show some age and perhaps one or two tiny nicks.  Missing teeth at the edge will greatly affect the price.
A crack will lower the price greatly as that type of damage may result in the loss of a piece.   A liberty bell was made for the Wold's Fair in Saint Louis.  It is one of a kind, but has a substantial crack, so much so that moving it was considered risky.   It was bought for about $5000.00 because of its rarity.
A piece having a stopper should be examined carefully.  Be sure the stopper fits the character of the piece.   If it is cut, the pattern should be the same as that of the main item.   A stopper should fit snugly, that is it should not wobble.   It should not sit too high or too low.   Many pieces have replacement stoppers.  
If it is a two part piece, the patterns of the two pieces should match.    Underplates and lamp shades are often without a match.   These are commonly referred to as "marriages".    Not only should the patterns match, but the size and weight of the objects should also match.   Sometimes a small plate may be matched with a small bowl, in which event the glass plate may be decidely thicker than the bowl.

Some patterns are more desirable to a large number of collectors than are others.  Consequently,  these patterns tend to bring a better price.  
Generally, American made pieces are deemed to be more desirable than European pieces, although this is not true of all items.  A great many stems available are from Europe, particularly Germany and Belgium.   These bring prices near those of American glass.
American, to most, is meant to be from the United States.   Several Canadian companies also cut glass and blanks were often made and cut on opposite sides of the border.   However, Canadian pieces generally sell for slightly less than those from the United States.
Signatures indicate the manufacturer and are more collectible and therefore often higher in price.   One must also be wary of counterfeit signatures which will lower the price.
Handles on items may have a crack at the point at which the handle is attached.   As handles are attached after the piece is made,  the glass may not  attach well if a difference in temperature exists.   These cracks are often referred to as "stress cracks" or "heat check",
The best advice is to examine a piece carefully, and if you have any questions, don't purchase it.
Auctions are a good way in which to establish market conditions,   Press the gold star below to access information regarding the value of auctions.

How Does Engraved and Intaglio differ from Other Cut Glass?

Cut glass was made by grinding away the glass with a stone wheel to form the pattern.           The pattern on engraved glass was done with either a copper wheel or a stone wheel.  The pattern was very shallow and often not polished, providing a greyish appearance.  Much engraving was of animals, flowers or scenes of people and towns.
Intaglio, on the other hand is deeply engraved and polished.  The patterns are most often floral patterns.   Intaglio differs from engraved glass in the deepness of    the pattern.
A unique form of engraved glass was introduced in the late 1800"s as  "rock crystal".   It had an engraved pattern, but it was very highly acid polished.  This caused the pattern to blend in with the glass as opposed to standing out.
True rock crystal  was quartz and consisted of deeply cut patterns.   Rock crystal in earlier glass also was heavy and deeply cut.
Rock crystal decanter showing heavy glass and polished pattern.  Possible about 1860.
Newer American rock crystal.  Glass is thin. The high degree of polishing makes it difficult to photograph
Prices for  rock crystal pieces generally  are about the same as for other cut glass.   Nicely engraved patterns, as would be expected, generally are of greater value.
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