Alex - there was a thread in March - "Selling a Motorbike"
I posted this there:
1. I have a yellow Tabian Baan, and a photocopy was all that I needed to furnish. The buyer was here on a 30 day tourist visa. We stopped at Immigration first. He was told that they would not give him a Residency certificate on a 30 day stamp - he had to have an actual visa from a Thai Consulate or Embassy. So, it is possible that your visa may be enough to get a certificate from Immigration.
2. We went to the British Consulate. They issued a certificate for him with a 30 day stamp in his passport. Cost was almost 3000 baht. We used a copy of my yellow book for his address.
3. He wanted to get a Thai license as well. What you can do is take the original of the certificate to one office for the transfer, and they will certify a copy of the certificate so you can use it at the second office for the license. No need to get 2 residency certificates.
I have no idea how long a certificate from the British Consulate is valid for, since we were using his immediately. The one from Thai Immigration is only valid for 30 days. You may have a problem if you have someone selling the bike for you after you depart.
So - as for your questions:
Legal side of buying/selling a Thai reg bike in Thailand
1, What visa/s do you need to buy a bike here and transfer the green book to your name?
You can buy a bike on any visa - even a 30 day.
2, What visa/s do you need to sell a bike here and transfer the green book to buyer's name?
As the seller, I was not asked to show a visa - just proof of residency.
3, What other forms/documents do you need?
Obviously the green book. Residency certificates for buyer and seller. In my case, I had a Yellow Tabian Baan, the buyer had to get one at the British Consulate. Immigration would not give him one because he was here on a 30 day visa.
4, Where /how do you do the transfer?
The MV office in Nong Hoi. The office on Hang Dong Road will tell you to go there.
5, Do both parties and the bike have to be there at the time?
In the past, the seller could sign a power of attorney and the buyer could go alone with all the documents. The form is available at the MV office (in Thai only). Not sure if that is true today.
The bike has to be there to verify that the frame and engine numbers match the green book. My bike was registered in Chiang Mai, and they had an index card with the history of ownership of my bike AND a photo of the bike model.
6, Anything else I should know?
You have to wait overnight to get the green book back.
And, of course, these were my experiences last December. TIT - yours may be completely different.
Good luck.