i have just bought a couple more coins on ebay after a couple of years of not useing it. i forgot how inaccurate the listings could be, a percentage is going to be genuine ignorance some is vaige or "im no exbert but i think etc" and the rest a pack of lies. i think the best solution is to ban sellers from grading thier coins and to let the pictures do the talking.
also i see in the listing the word "Rare" i dont look at it.
You are right that "rare" is just a term for "overpriced".
As to grading, I think everyone (including evil sellers) should be allowed to give an "estimate", provided they have a basic understanding of the scale being used. I think the burden has to be on the buyer to judge for themselves whether or not the coin meets that estimated grade.
If someone outright lies (or fabricates) and says a coin is "Brilliant Choice Uncirculated +++Luster RD", then that's their representation of quality. Under the common law and uniform commercial code of most US states, the salesperson of any item won't really be held to that description, because it is considered "puffery" or a "sales pitch".
If the seller lies, however, and says a copy or counterfeit coin is the real thing, that's where most US states' laws would step in and say that the seller is being deceitful.
I think that because Ebay is based in the United States, and sees a vast majority of its customers in the US, simply conforming their rules to basic, generally-applicable US law regarding the sale of goods is easiest and best. Now, of course, a seller in France or the UK may have to ensure their listings conform with consumer protection laws there, but that's really what places like ebay.co.uk and ebay.fr are for.
[In all fairness, i do sell some on Ebay; I count myself mostly as a customer because I sell perhaps one coin per month, whereas I buy perhaps 20 coins per month on Ebay]