01Count every cost, not just the grading fee
Grading a card costs more than the grading fee. There's what you paid for the card, shipping to the grader and back, insurance, and the selling fee when it sells. On eBay, the final value fee on most trading cards is about 13%.
A flip only works if the graded sale price beats all of that. The calculator adds it up so you can see what's left.
02Don't plan on a 10
Most cards don't come back a 10. Look at the card closely, centering, corners, edges, and surface, and be honest about your odds. Then check the 9: if the math still works at a 9, it's a much safer submission.
Expected profit weighs each grade by its chance. If expected profit is negative, the card is a gamble, not a flip.
03Use sold prices, not asking prices
Asking prices tell you what sellers hope to get. Sold prices tell you what buyers paid. Use recent sold sales for each grade, and look at more than one.
Slabfy's Flip Finder does this for you on every card: it pulls the sold sales at each PSA, BGS, SGC, and CGC grade and shows the flips that make money.