It depends. Some people know their plants; other just want your data (aliexpress, ahem...), and will send you anything instead to justify the order. You could end with invasive species (just because there is plenty of them), or sowing canary's food.
For a newbie, is safer and easier to start with commercial packed seeds.
Oh yeah, that's true. Even at an exchange, seed fair, whatever, I would probably still only buy seeds from an actual vendor. I'd never considered buying something like seeds from an eBay seller. But yeah, lots of organic heirloom varieties are packaged for commercial sale, eg:
Seedlings are different since with a bit of experience you can tell what most plants are, at least within the broad family— you might end up with hot peppers when you expected sweet ones or something, but you're not going to get marijuana when you thought it would be tomatoes.
For a newbie, is safer and easier to start with commercial packed seeds.