Some help with an English Crown

Yes, based on my past experience with Spink, their grading standards in the book are vague at best (though to be fair, if you were looking to cover 2,000 years of coinage struck under very different methods of manufacture, you'd have to be vague).

I developed my "grade on the fly" skills (such as they are) from the parameters set forth in the front section of the Krause Standard Catalogs of World Coins. When memorized, those general guidelines from Krause can get you most of the way towards being able to grade just about any coin from anywhere within a reasonable degree of accuracy, though of course where specialized standards exist, they supercede the more general ones like Krause.

Of course Krause does not use numerical Sheldon Scale grading like the third-party grading services do. I just use my Krause-based "grade on the fly" instincts and then mentally tweak them accordingly if I'm going to guess a numerical grade, like I did here. So my intuitive grading is partly based on Krause standards and partly on TPG standards. As with anything, one just develops an instinctive "feel" for it after a while. And as with all instincts, it's inaccurate sometimes. But I'm generally pretty close.