I just bought a second-hand scooter, yamaha mio 115cc

I got the new square paper written 2556

and the salesman (scooter shop) promised me he will brung the FREEN BOOK in my name in 3 more days

Is that enough or do ineed to get more registration and insurances??

All those documents are in Thai and the salesman knows so little English

You will need to furnish him with a certificate of residence before he will be able to put any vehicle in a Foreigners name

Bike or car/truck

You need this to buy,sell or register any vehicle in your name. Also to get a drivers license if you are not a Thai

PS: although I have not bought used so,

Perhaps in your case you will go with him to transfer the name in the green book to yours.

But I believe you still need the certificate of residence which you may obtain at your country of origin consulate or Thai immigration

Example of prices are US Consulate $50 USD Thai Immigration I think is 500 Thai Baht

Certificate of residence + signed copies of your passport

That's all you need to get the m/c registered in your name.

(For a foreigner to sell a m/c in CM you currently only need passport and green book)

No need for DL of any type (though you might need one to legally drive the m/c depending on your VISA). No need for you to go with him.