Grading - not very easy

Being new to this with grading coins, trying to grade my own, I find this a bit tricky. The guide in Numisdoc is helpful, but vague sometimes. Maybe you can help?

- A 60 year old coin of copper or brass with no visible wear, but which is green/black from oxidation (a rather natural process) - would that be VF or XF? How discoloured should it be before being downgraded?
- Grease from fingers seem to speed up oxidation. If I have a newer coin which is looking really nice, but someone has put his/her thumb on it, and there is clearly a fingerprint on the coin (where the grease has sped up oxidation) - how much does this matter?
- Coin grading seems also to be about wear and tear. In Numisdoc --> Coin grades under VF it says "At least 75% of the coin's original design is apparent", how can I tell this is the case if I don't know what it looked like when new? Are there any particular things one should look for?
- Scratches, how will this affect grading? If it has some minor scratches here and there, but all details including hair are sharp, could it qualify as being graded VF, or even XF, anyway.

just like you have surmised, there is no hard and fast rule. it is a skill which you develop over time. the best test is to ask few other collectors whether your VF is his XF or F or VG. The concurrence of several experienced collectors would show that you are on target.

wishing you happy collecting and skilfful grading.

please read it as skillful and not  skilfful. lol.

Perhaps if you were to put up some pictures of coins you are trying to grade then you could ask for the opinion of other members and see how that compares to your own ideas. But also remember that, as pjthayil indicated, it is not an exact science and even experienced collectors may disagree on a particular coin's grade.

Took some pictures yesterday, then noticed I can't find the lead to connect the camera to the computer...

But found this: http://www.coinsandcanada.com/coins-grading.php?grade=25-cents-1911-to-1936-George-V&id=7 - seems quite clear, but only if the coin is uniformly worn.

So what is not so clear is if there is, for example, a scratch in a otherwise perfect coin. Or if the coin looks great, if it weren't for a bunch of tiny, little, wee scratches all over.
Or what happens if it's not worn, but dirty and the dirt seems quite stuck.

How important is that?

They mention a grade on the above page not present on Numista, namely MS-60. "...ugly, dinged-up, bag-marked, ill-toned...", they say, but still mint with no wear. And still a high number. Should I understand it as if wear is the number one priority to look for when grading?

If I only could find that camera cable