I had two misses. First, I was sent an incorrect size seatpost (ordered 31.6, received 30.9). Second, they missed throwing in the chainstay protector. Even though Peter had already left XMIPlay, he did everything he could to make it right by offering up shipping the correct post and chainstay protector - I turned down the post, as I had already bought one elsewhere.
That being said, I'm still happy with the overall process and I'm playing around with the idea of doing another bike for my son if any of these suppliers can come to the table with a 14"-16" frame.
Recommendations -
Confirm, then re-confirm the entire order before PayPal'ing any money.
Confirm, then re-confirm stock availability of the components you want.
See if you can put in writing that if anything is missed or incorrect, the supplier is responsible for making things right. This may not hold any water, but can help - none of this "Customer pays shipping on missed/incorrect parts", next order BS.