When looking for seeds on eBay I follow a few easy guidelines for myself. (e.g. Where does the plant grow that produces the seeds for sale, is the seller in that country/location? Because if not I doubt they are traveling by plane or far by any means for a couple bucks worth of seeds.)( look for consistency in photos, watermarks, etc, description, do they know what they are talking about, ask for photos of source plant etc etc etc. or are you buying "nepenthes, bonsai, balcony, giant clip raidiation protection plant seeds"? I mean we all know to steer clear of that I hope. I have ordered many seeds from many people online as they are inexpensive and I figure it's worth a shot fake or not. After obviously doing my due diligence to determine to the best of my ability that they most likely aren't wild collected. With that being said, I have never been disappointed in a U.S. based seller (obviously not collecting nep seed in the wild.) seeds from Europe have also been legit just with much less germination (assuming travel, etc,etc) from Indonesia/Asia. I have received seeds that I frankly have no idea if they were legit or not, no germination.
This is my experience. Uncut. If you are thinking any more into than this you should just play it safe and buy from those you know/ been provided solid feedback.