Consider
The PSA 10 premium on Kingdra-GX #66 from Dragon Majesty is modest. At $13.10 raw against $160.00 for a PSA 10, that works out to 55% ROG. A 9 instead of a 10 would likely wipe out the margin here, so be honest about condition.
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 5-in-10 shot (54%) at a PSA 10 for this to pay off.
A PSA 10 puts you $56.90 ahead. A PSA 9 still sells for $37.50, so a disappointing grade costs you $65.60 rather than everything you put in.
Among the 34 cards in Dragon Majesty with PSA 10 sale data, Kingdra-GX ranks 24th for Return on Grading and 23rd by PSA 10 price. Of the 6 Rare Ultra cards with PSA 10 sales, it is 5th for Return on Grading. The median PSA 10 in this set sells for $260.00. 18 of the 34 clear a 100% Return on Grading.
