Worth Grading
The grading maths works on the Rare Rainbow Reshiram & Zekrom-GX from Cosmic Eclipse. At $257.54 raw against $680.00 for a PSA 10, that works out to 96% ROG. Not spectacular, but the margin is real once fees are covered.
Most grading maths asks you to guess your odds of a PSA 10 first. This works backwards from the prices instead and tells you what those odds would have to be.
The number is different on every card. It's how confident you'd need to be that this copy gems before grading pays for itself, so 20% means roughly a 1 in 5 shot and 50% means a coin flip.
Grade it if you rate your copy better than that, leave it raw if you don't.
It assumes a 9 is the worst you'll get. Centering and edge whitening send plenty of modern cards back at 8 or lower, and that's not priced in here, so treat this as the floor of the bar rather than the whole of it. Selling fees aren't counted either.
(cost - PSA 9) ÷ (PSA 10 - PSA 9)
You need at least
a 1-in-4 shot (24%) at a PSA 10 for this to pay off.
A PSA 10 puts you $332.46 ahead. A PSA 9 still sells for $242.08, so a disappointing grade costs you $105.46 rather than everything you put in.
Among the 113 cards in Cosmic Eclipse with PSA 10 sale data, Reshiram & Zekrom-GX ranks 50th for Return on Grading and 14th by PSA 10 price. Of the 14 Rare Rainbow cards with PSA 10 sales, it is 3rd for Return on Grading. The median PSA 10 in this set sells for $241.50. 48 of the 113 clear a 100% Return on Grading.
