I am uncertain whether he is just being safely conservative in his grading. He auctioned off several dozen m101-4s the past couple of days that were listed mostly as low grade and filler but clearly are not. That set has wide tolerance in measurements, and I believe he listed them as fillers because of this, although I agree with others that if he believes a card is trimmed he should say so. If it fails to measure or he is uncertain, just indicate that or put a question mark in the listing. Frankly, when I first went through those offerings and saw so many low grade filler descriptions I thought someone had just forgotten to change the description in the title.
Here is an example of what he called a filler:
This card has somewhat narrow side borders but is within tolerance and is not trimmed. It also has some discoloration on the back, but so do hundreds of graded examples that do not discount for this. Scans can be deceiving, but unless that is paper loss or glue residue on the back there is no way that card is a filler. Absent those problems it would grade EX or so, although these days the cost of grading does not justify its submission. Oh well, good for the buyer I guess.
*** Just to be clear, I have purchased many cards from this seller and believe him to be one of the good guys.