I'm A Newbie - Why Do Prices Fluctuate So Much?

Hi, I'm currently looking through my great grandmother's stamps.
I'm wondering why prices seemingly fluctuate so wildly?

For instance, the following stamp has sold for high prices:
https://www.ebay.co.uk/itm/British-...047675.l2557

https://www.ebay.co.uk/itm/BRITISH-...AOSwAGFcUrm7

Yet it has also sold very, very cheaply:

https://www.ebay.co.uk/itm/British-...AOSwt3hcHhfP

https://www.ebay.co.uk/itm/BRITISH-...AOSwFoNcKCU4

Why does the monetary value fluctuate so much?
To me, the stamps all look exactly alike.
I'm only starting to learn the terminology (MNH, NH, etc.).
However, the linked listings' stamps all seem good condition.
I've also noticed other stamps whose prices vary.

Any sound explanation?

Thanks.

They are not the same stamps. Catalog numbers are different.

OH95: welcome to the Forum. What makes the first two differ from the second pair is the perforation. Meaning, the number of holes on each side of the stamp. The stamp with 14 holes on top by 13 holes on the side is much more uncommon that the other one.

First listed as mh, nice centering. Second listed as lh, nice centering. 3rd. And 4th. Off centering but basicaly different perforations ; therefore the bottom two are totaly different stamps than first two listed.

But on ebay you will find similar items selling for different prices. The depends on what the seller wants to achieve - fast sale or more profit.

You can just look a modern US Mint stamps. Some of the same issues sell for below face value and others try to sell it for a significant uplift.

OH - Hello. If you get hold of a Gibbons Commonwealth catalogue, you'll be able to see the varieties of each "identical" stamp - chiefly differences of perforation or watermark. Bear in mind that the Gibbons catalogue prices you see should be multiplied by 10-20% to get a rough market price. At the bottom end of the catalogue price scale, stamps will be worth a penny. In the UK, the standard nomenclature for condition is different. "Unmounted mint" means never hinged, "mint" means currently or previously hinged and "unused" means uncancelled, but without gum.

In the UK you can get the Stanley Gibbons catalogues from the library. If they haven't got them put in a request. Assuming the your Grandmother collected GB get the SG Great Britain Concise. If you aren't intending to collect stamps yourself ask around and try to find who is a reputable dealer and ask them to look at the collection. many dealers can say within moments whether a collection needs to be studied more closely to get an idea of value.