Let's say I was to buy a bike in a different province than I live in, bike unseen but sent by transport to me. What documents would the seller need to send me copies of in order for me to get it registered in my name, or the wife's. Bike is currently registered in the seller's Thai wife's name.

I'll be curious to know the answer as well

Based on "Bike is currently registered in the seller's Thai wife's name"

1. You need a signed copy of the current owner's id card (both sides), the actual green book, and a signed authorization to allow you to transfer the bike without the current owner being present (available foc from the transport department).

and

2a To your name you need proof of address from immigration, and a long term visa (but dependent on the "local rules").

or

2b To your wife's name she just needs to go along with her id card.

Thanks for that 12. Much appreciated.