Sorry I am new to name-buying, can you explain for me? What does ready to transfer actually mean?
And as for vouches I have only bought GP here once before so I understand your concern.
Lets say you purchase the name "Pinocchio" from me. You would like to put this name onto your account, because its more secure. Its best to have me, the seller change the name to avoid any chances of having me message jagex and saying something like "omg i was hacked1!!!!". They will say "you changed the name. nothing we can do.".
so anyways, you change the name to scar123
then you have to wait 30 days or so to change the name again. It is now ready to transfer.
When you change the name again, the name "Pinocchio" will become available. Its best to wait until random times of the day, after updates, a while after original xfer date to avoid name snipers. Snipers will set up auto clickers for names they want and you wont stand a chance in transferring your name.
I've sold some other stuff but i dont really keep track because afaik vouches dont really mean much around here until you get into higher numbers. Even then, thats questionable. Its all about judge of character honestly. Even then, social engineering is not hard. Its all a gamble.

Though I do have a history and can get vouches if needed. Or you can just search my posts, doesn't matter. I've sold a few names, pures, just take a look around.