you should have
Take the printout of these forms and get it duly filled and signed. And submit it in the RTO for a change of ownership of the bike. Form 28 and Transfer Deed is not mandatory for sale/purchase but Form 29 and Form 30 are mandatory.
Transfer Deed
Transfer Deed is the certificate the seller should possess to have no legal liabilities on the bike in future. 2 original copies (not photostats) of Transfer Deed should be taken. Engine Number, Chassis Number and Registration Number should be written in that. Revenue Stamps should be pasted on them and signed by the buyer. Both buyer and seller should posses the forms.
Other Documents
Given below are other documents the buyer should get from the seller while purchasing a bike.
RC Book [Registration Certificate Book]
Ensure that the RC Book is in order and the engine and chassis number printed in the book match with those in the bike. Also the name of the owner should be correct, once the sale is through the RTO office will change the name of the owner to the new buyer's name.
Insurance Certificate
The bike should have a valid insurance certificate covering the period of sale. Once the ownership of the bike is changed to owner's name ,ensure to change the name of owner in the insurance certificate also. This can be done by giving a written request in the insurance company. If the insurance is lapsed the new owner will be liable to pay the fine for the time without the insurance, so ensure that the vehicle has insurance.
Tax Receipt
The bike should have a valid tax paid receipt. These days most vehicles have life time tax paid, this is usually for a duration of fifteen years [varies from state to state]
Pollution Certificate [Pollution Under Control Certificate]
Even though this certificate is mandatory for vehicles which is more than six months old, unlike insurance certificate buyer need not pay the fine for the period bike didn't have the certificate. So in case the seller doesn't have one, buyer can go get a new one, once he/she has the possession of the bike.