A General Guide to Grading Coins
Grading coins is not easy and many sellers will conveniently tell you that it is a matter of opinion. It is true that it can be quite subjective; but there is a professional concensus amongst coin collectors/dealers in regards to grading coins. That's why many numismaticists specialise, because each coin for a given country has a different grading standard from another one, even of the same era.
Coins from an earlier period, let's say British ones, will also have an entirely different grading standard. For example, Gothic Florins will not be graded as strictly as Jubilee ones (as in the case of Victorian coins), because Gothics are rarer and have worn a lot more over time compared to Jubilees. This is because of the design; each type of coin is designed differently.
So, be careful when buying on eBay; the professional collectors know how to grade every British coin and are not in the habit, like the amateur is, of overestimating or underestimating the grade. Poor or misleading pictures can also make things difficult for the buyer. If you get your estimate wrong by just one grade level, then you could be looking at a big difference in the price you pay or the bid you make.
My scheme below is still subjective, but I have made it as good as possible to help people get as accurate an estimate as they can. It is in rough draft now, but eventually I will revise it and make it better and I will try to provide picture examples as well.
It is my own scheme and I will sometimes refer people to it from my coin auction ads (mostly UK). I tried to be as objective as possible and I did it in order to reduce the subjectiveness of grading on eBay. Many coin sellers will overgrade their coins and it is always wise to bid one grade below what is said or what you think you see in a photograph in an auction ad. The grading sheme will only really apply to British coins from 1816 - 1954 inclusive.
Coins are three dimensional and you really can't see all the detail and grade until you get them in the mail. Sometimes supersize pictures can show a lot of the coin's detail, but these can only be used for expensive coins. I use fairly high scanning resolution for my coin images and I also explain certain points about the fine detail. So, I feel that I can get away with a non-pictorial grading description here, at least for the time being.
I find that other guides are lacking, vague and inaccurate. I'm not saying that mine is perfect here, but at I think I am on the right track in terms of the need to provide more divisions in order to make a better value assessment. I will be coming back to this page from time to time, so that I can edit it and eventually revise it to the point where it is as complete as possible.
It is often helpful to provide pictures as examples for grading coins, but each coin group is different and some coins are not graded as strictly as other types. It is all relative. In this case, the grading scheme below will be sufficient for most purposes. So, for now, I have referred people to the Spink guide and possible websites, at the bottom of this page, if they need to see pictorial examples.
I don't know of any exhaustive photographic guides with hundreds of pages of pictorial grading. This may sound a bit much, but it may one day be a good idea, because each coin wears differently. If you are slightly out on your grading analysis, you may bid too much along with another person and end up paying too much for a coin.
The grading scheme below is fairly straightforward, but an explanation (key) of some of the explanatory terms is below; at the end of the article.