Hopefully your breeder does periodic fertility testing or hatches their own eggs enough to know if they have issues, fertility is measured as a percentage so you can’t use it to say x or y egg is definitively fertile, only out of ten eggs 8 should be fertile if 80% fertility, but you also get variation within batches too, you could have only six or all ten.
Shipping is a gamble, but sometimes the only way to get a species or genetics or breed you are interested in, plan for a disaster but also be ready if everything goes great. I’ve ordered 40 eggs and got 10 viable chicks and also ordered 24 eggs and got 24 chicks (they sent extra eggs in that batch), and it was a little bit of a scramble to house that many chicks when I was expecting a dozen. Besides lower hatch rates expect mutant and deformed chicks like wry neck or scissor beak, every shipped hatch has had a mutant or three while home grown hatches rarely do.
I have discovered I have a quail addiction but no risk of a gambling addiction, even be it shipped eggs! The more anticipated or expensive the eggs, the worse your hatch rates (Murphy’s law!).