I think in those circumstances I would definitely drop them a line and let them know what's up. At the same time, try to see the situation from the other guy's point of view. They might sell hundreds of seeds a week and never get complaints. They sell to growers of very different levels of growing experience and ability. You see where I'm going with this? But they might have got a bad batch of seeds for some reason, and they might appreciate their customers letting them know.
I think if you approach the situation in a reasonable and respectful manner there's a good chance of a favorable result.