So a wandering trader came in on a LAN world (I wasn't hosting) and he really wanted to sell me seeds...
I'm not sure if this is intentional or not, but if it is, there should be a limit on it. You don't want to talk to a wandering trader and find that all of his trades are seeds, or buckets of pufferfish, or something else crazy like that.
Not completely sure how to reproduce this one, but you could probably spawn some in and check their trades. This happened in a Survival world, the seed is [Testificate] if that would help for some reason.
Also, please note that he shows up as "Wandering Trader - Novice", even though wandering traders don't have ranks or anything, unless he's part of a worker's union or something.