when seller state otr price, but the insurance is compulsory to buy ourself?
or can use seller insurance

Usually insured already.

the insurance premium is alredi included in the car price..normally they have appointed certain "unpopular " insurance agent ...

means the insurance under seller name or new buyer name

u mean 2nd hand car or new car ?

if new car , of course under ur name ....

2nd hand car

Cars normally once sold the insurance for that car is cancelled, who going to pay the premium for car they don't own anymore right.

OTR means everything paid up and the car can be driven on the road immediately

yeap this is correct, for insurance you have to buy your own insurance if you dont have a previous car OR transfer your previous insurance NCD to your new car to get discount on the insurance based on your NCD level.