These
'Collectorisms' come into play here...
197. Graded Exchange Rate
The pursuit of a mathematical equation to forever solve vexing problems such as, “If a PSA 6 usually sells for X amount, how much less should I pay for the same card in an SGC 6 holder?”
See also: Whifferential (in beta testing) - the advanced formula that takes into account what grade you’re convinced your card will receive, in order to determine what (much lower) number it will actually receive.
See also: Onomapopeia - the litany of curses that flies out of your mouth the moment you find out what horrible grades your cards received.