I don't know why PSA's sell for more, probably a "self fulfilling prophecy" because people think they are worth more and should sell for more so they pay more for no other reason than that. It's certainly not for PSA's beautiful holders in comparison to SGC
I keep hearing about PSA being stricter in their grading. I disagree on that, at least in the low to mid grade cards say grades 2-6. SGC has been crazy picky on some of the cards that I have had graded and when it comes to any type of paper loss I've found them to be much harder on that than PSA. I've submitted to both many times and have had many more comparison cards. Depending on the issue(s) that a card may have that usually determines where I send it (that and whether or SGC has a good monthly special
) If the card has a small amount of paper loss I can be certain that SGC is going to grade that 1.5 or maybe 2. I can usually get a 3 out PSA all other things being equal.