I do not think that you can access that information online. You will have to call Tivo customer service.
If you give them the service number from the box you are interested in buying then they will be glad to give you the basic information about it(like, does it have a lifetime subscription, etc.).
To my knowledge all Tivo boxes are eligible to be transferred.......unless it is stolen or something.
p.s. I do not know which type of Tivo you are interested in buying, but I am about to put one up for sale. I have a dual tuner Tivo with a 160 gig hard drive. It is only about 4 years old and it is in perfect condition. I even have the original packaging.