I'll break these down into different posts for (1) Ebay (2) Online and (3) Retail. Of course there will be overlap.

Where possible, the names of the plant(s) purchased might be useful. If you have any experiences as to whether their plants are correctly ID'd that's a big concern, so please mention it.

That said, I think I've only bought a Passiflora from one source on Ebay:

Potato Rock Nursery: Very nice P. tripartita var. mollissima for very cheap.

Others:

I've traded for a couple plants with Kevin, who posts here occasionally. I know that he's sold a few plants as plants-2-you . I would expect his plants to be very high quality and correctly ID'd. Kevin knows his stuff--another reason to buy from him.

I've never bought from Strange Wonderful Things, although I know people who have (and are very satisfied) and I know a couple friends of his. His friends are people whose judgment I trust and they have nothing but good things to say. He sells a lot of very nice stuff and from all indications it is very high quality. However the auctions often get bid up to very high levels. You might want to check and see if you can get the same plant for a better price from another high quality source, particularly Grassy Knoll, before joining the frenzy.