I've had some luck at times where the seller actually under graded all the 45s I ordered, but the next time I ordered from the same seller they were graded correctly. Yes, I have bought some over graded 45s, but worked it out with the seller. This was on Discogs.
I hear what you mean, but it sounds better from my own computer. However, I was told by an expert (Bosshoss) that it is because the record is warped and the tonearm is having trouble tracking it. It played better when i increased the weight to 3 grams.