Consider
Whether Dialga-GX from Forbidden Light is worth grading comes down to condition. Raw copies trade around $8.49 while PSA 10s sell for about $125.00, a 27% Return on Grading. Only send it if you're confident the copy is a genuine Gem Mint candidate.
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 7-in-10 shot (69%) at a PSA 10 for this to pay off.
A PSA 10 puts you $26.51 ahead. A PSA 9 still sells for $38.14, so a disappointing grade costs you $60.35 rather than everything you put in.
Among the 55 cards in Forbidden Light with PSA 10 sale data, Dialga-GX ranks 31st for Return on Grading and 31st by PSA 10 price. Of the 8 Rare Holo GX cards with PSA 10 sales, it is 6th for Return on Grading. The median PSA 10 in this set sells for $151.50. 21 of the 55 clear a 100% Return on Grading.
