USED RECORD GRADING- What's the Problems?

While the current grading regime is far from perfect I can’t see how any alternative is better. Especially as each of us is different in terms of what we expect. For example I’m really quite tolerant of tics and even light scratches but even a hint of hf breakup from prior mistracking sets my teeth on edge. Also depending on the setup different problems will manifest so even play grading will not mean the same thing to different people.  

Good luck w/ that. Even play grading is subjective. In some cases, I'd prefer that the seller not play it or purport to clean it. Just spin it to tell me whether it is warped. I had one seller tell me when i asked about warps: "You'd have to be an idiot to sell warped vinyl"
Guess what? 
I try to do the due diligence before I press buy- i have a dialogue with the seller thru the messaging system if a platform or via email if a store. The responses are often telling. 
I consider myself lucky. I've had some misgraded records but overall, I've come out OK on balance. I also do a serious cleaning when they arrive or at least before they get played. And sometimes re-clean, which can help remove grunge that sounds like groove damage. Sometimes it is groove damage. 

When seller with good feedback says NM I automatically assume that it will be VG+, and in 90% of cases I am correct. When it says VG+ it is quite a range that I got - from VG- to true NM. So I usually expect VG+ record and the right to return it. No need for new grading system, it would only confuse the issue further.
I talk to sellers too in some cases before buying.