G'day Mollydog
If I was just doing a ride in VN I would rent.I cant advise on Hanoi but there are hundreds of bikes available to rent in all the tourist city's in the south. Negotiate price down to what you are prepared to pay.
Usually the shop will want to hold your passport but as it can be required to book into accommodation etc another form of security maybe organised.
To avoid problems(confiscation)with the police you are required to carry your Vietnamese licence, bike registration paper(in the owners name is fine) plus it helps to have motorcycle insurance & money.The money is the important one.
Everything will depend on the mood/finances of the police at that particular time. Some with no English will just wave you away, others will get the dong sorted somehow,then you will get the cop with English and you just go for your wallet.
The main thing to avoid is having the bike loaded on the police truck and taken to the impoundment yard. From there it can get difficult ,expensive, and extremely inconvenient.
When I lived in VN years ago the usual police donation was 40,000vnd and it was a regular event. This trip it was only the once but 600,000vnd.Inflation ?
Thirteen years ago I sold a Suzuki 110(registered in my wife's name) to a Viet mate, the same bloke still has it, still in my wife's name,97,000km on the clock.
Vietnam-------sort it out as you go along. Rules & regulations :confused1:
Love it, Macca