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Josh K.I think what scott says is correct - in my experience, sgc has, at time, gone little easier on corner wear while psa is really lax on creases/wrinkles.  I will say that one area where sgc is unquestionably stricter is paperloss.  Ive seen psa 4s and 5s with paperloss on the reverse (more than just a spot).  Im not sure Ive ever seen a card with paperloss graded higher than a 30 or 40 by sgc.