Let me know if you want me to name names.
I recently bought "seeds" of Mitragyna speciosa from a couple different vendors. The first sent absolutely empty pods. At least they refunded me when I complained. The second seller sent seeds that just looked underdeveloped. Sure enough 0% germination.
Lots of palm seeds over the years were totally worthless. Even rotten seeds from large, well-known vendors.
Tons of fruit seeds from other big name sellers, with horrible results. Apparently vendors don't commit to rotating old stock with new stock, and prefer to just off-load completely old dead seeds to unsuspecting buyers. I've had so many bad experiences over the years, that I'm not sure I'll ever buy seeds again from any big seed websites. Things like vegetable crops are usually pretty reliable, but forget about palms, fruit trees, and other rare plants. It seems none of the vendors even check their viability.
One thing I've been keeping an eye out for now for a few years is Musa ingens, the giant banana species. A quick internet search yields a few results, but the prices are so ridiculous (like 3 seeds for $14) and I just assume it's from some batch being resold over and over again from seeds that could very well be a decade old...
I mean you can always ask a seller how old the seeds are, but what do you think they're going to say, "Oh yeah those have been laying at the bottom of my sock drawer for the better part of two decades. I don't even remember who I bought them from or when they were collected."