Hanoi vendors are not anywhere close to as aggressive as those in HCMC. Northern people are different from southern people. HCMC is a highly energized mercantilistic place and was so even when it was called Saigon.

Singapore is a completely different kettle of fish. In Singapore you won't have any more aggressiveness among vendors than you would in the USA. It's an extremely modern city probably more advanced in most ways than average US cities. Definitely cleaner.

Based on the additional situational circumstances you described, it's an easy decision. Get the HAN/NRT trip refunded and go to Singapore this time.