If stamps in a collection from any era at any time and not paid for stamps from a dealer then in most case the stamps will be in used condition and the collection will be of little value, however a collector that paid 1 or 2 shillings for a stamp over 60 years ago may well have stamps that are worth 1000's of dollars for each stamp today.
Above is a 1932-1945 C of A Watermark 6d Chestnut Kangaroo on Map of Australia this stamp is in VFU (Very Fine Used) You can clearly see the circular cancelation stamp showing that is obviously in used condition though the stamp is above average since it still includes all perforations around the edge of the stamp as well it is very well centered.
Generally Stamps being sold on eBay should be described to the best of the ability of the seller listing the stamp or stamps though if able to obtain any stamp in the condition described in the listing for less than 50% of it's catalogue value then it should not be disappointing to the buyer if the stamp is in average condition. When placing bids on any stamp the bid placed should reflect the condition of the stamp as well as the description, knowledge and reputation of the seller listing the stamp. In most cases the buyer should be satisfied with the item they purchase and the stamp should reflect the description given in the eBay listing at the time of sale.
All sellers and most buyers should know that mint or used stamps will attract a higher catalogue value than those stamps in used condition. Mint stamps need to be post office fresh, that is they need to look about a year old if issued within the last 20 years and should look around 5 years old (slightly aged & toned in color, gum may have some cracking) if 60 years old or more. Pre Decimal Mint Stamps (Pre 1966) that have hinges (MH-MINT HINGED) or that are (MLH-MINT LIGHTLY HINGED) are usually acceptable to most collectors this is understandable as stamps collected in the era where contained in albums which only allowed for stamps to be secured in the albums pages by being fixed in place with a hinge. For this reason it is some what rarer to find pre decimal stamps in (MUH-MINT UNHINGED) condition, though at present MUH stamps are still available on eBay on a regular occurrence though I believe with stamp collecting as a hobby continuing to grow as it has over the last 10 years it will not be long before premium MUH stamps will be harder to obtain.
Above is the reverse side of a 1928 3d Blue Kookaburra (4th Australian Philatelic Exhibition, in Melbourne) this stamp is in MUH (Mint Un-Hinged Condition) or MNH (Mint Never Hinged).
Some Collectors also may choose to describe MUH - Mint Un-hinged stamps as MNH - Mint Never Hinged, obviously if a stamp is Mint Un-Hinged it has never been hinged, though a lot of people still choose using MNH to describe their stamps though MNH is not recognized in any philatelic community or organization.
It is already common to see MUH stamps reach prices well over there catalogue vale. Some educated buyers waiting for highly sort after stamps (Kangaroo, KGV heads, Robes, B.C.O.F sets, Silver Jubilee sets for example) are well aware of potential investment and increasing catalogue value of certain stamps as they become harder to obtain.
Above is the reverse side of a 1913 1st Crown over A Watermark 1 Pound Brown & Blue Kangaroo on Map of Australia this stamp is in MLH (Mint Lightly Hinged) you can clearly see the mark left from the hinge at the top of the stamp though the hinge itself has been removed.
There are some Pre Decimal stamps can be more valuable if the stamp has no Watermark or has a different die variety (Die variety usually a difference in the shade of color) usually because their was less of the No watermark/Die variety of the stamp produced so making it harder for anyone collector today to find. The stamp has perforations these are the small teeth like looking edges around the stamp, these perforation can also increase the value of a stamp as some stamps where produced with more than one amount of perforations (either height or width) around the stamp. Also if a stamp is missing or has less than half length of each perforation the value of the stamp will normally be 10% less of its catalogue and less again if the stamp has been cut or torn in anyway.