Why do some items go for a fortune and an identical or a similar item get sold for next to nothing?

[boogiewoogie]

Any ideas? Sometimes I suspect shill bidding when there seems to be lots of bids for something and further down the list, there is another item which has 1 bid and sells for 99p. Doesn't really give me a good idea what an item is worth.

[Pingpong]

if two people want an item there is demand and if they both bid the price goes up. Once one person has won the item unless another person comes along quickly there is only one person bidding so they get it cheap.
I sell the same item over and over and if I put the items too close together in the auction I rarely get a better price for the second one.
It is very hard to gauge sometimes what an item is worth. Even when you look at completed listings the price will often vary depending on the time of day the auction ended. Eg the item I sell I put it to end in the evening as more people are at home and it generally gets a better price. I often seem others listing in the early morning and generally speaking they get less.
Sorry I'm speaking in very general and broad terms but these are just my experiences/observations

[PurpleFrog]

Sometimes it also depends on the categories where the items are posted. If buyers only look in the certain places sometimes identical items are missed, whereas a global search will find them.