From the images I can only say 'plausible'. If the seller isn't asking an exorbitant price then the precision of the answer doesn't matter; if he's charging through the nose then we need better pics.

 

Then I will try to get the holster if the price is right. Thanks a lot for your evaluation.

 

I was able to get the holster for little money. Based on the better photos, can you tell approximately when the holster was made?

 

In my opinion, however, the holster was not made for a Colt Pocket 1849 or 1862 Police Revolver, as the seller said.
Here with a Pocket 1849 revolver inserted.

 

And here with an 1851 Navy with small rounded trigger guard. A 1851 Navy with a large trigger guard should fit, or what do you think?

 

The 1849 obviously isn't a fit so the 1851 seems to be more likely.
Without some sort of makers mark, when and who made it is probably never going to be known.

 

What do you think, was it made before or after 1900?

 

It's a Wyeth, likely early 20th century from the better images shown now, because of the sewing. Wyeth made for the mass, mass market that was catalogue houses that resold these products, and did not make any holsters for a specific pistol; instead, in general sizes. We can tell it is for a revolver, and we can make general choices based on barrel length that has been provided for; so I'd say your holster is perfect for any revolver that fills the entire pocket in this way:

This one is marked for the catalogue house (Wyeth sold in dozen lots only, per size) and is marked '38' '4' which in those times meant a small to medium frame DA revolver with a 4" barrel.

That's all the information they supplied even in their literature, with as you can see, a few exceptions: