Twice this week I've ordered books from deals offered in the Bazaar, and the book ordered has gone to someone else. Luckily, both times the person emailed me and said they didn't get the order and I was able to cancel and reorder, but I don't know how it's happening? All I can think of is that maybe I have clicked on the book in their list for further details and then ordered it? If I did that, would it go via FIFO rather than to the person on whose shelf the book? I don't like having to cancel orders, but on the other hand, if I'm participating in a 2/1 or 3/1 deal, I don't want to order it alone from someone else.

Yes, if you click into the details (or even just hover over the book and click in that yellow pop up window)  you will order from FIFO, not that member. To order from them you need to be on their WL and use the Order button on the right. You can tell you are getting it from them because after you click on the order button you will see their name at the top (right side I believe).

I usually click on the PM button on the request too to make sure that the correct person is getting the order and I watch that until the request is accepted in case the person offering the deal cancels for some reason because the orders will go to the FIFO line then too.

Thanks, that's what I figured when it happened again.