bidding etiquette

..even if seller accepts bid?

I believe someone linked a case that showed that in NY unless u signed a contract it isn't a deal.

get a lawyer to confirm.

Yep it works for both sides of the street.
It's all about a signed contract.

Even in contract, sometimes their are terms or loopholes that could possibly be exploited to gwet out of a contract.
A good lawyer is a must.

You can make offers, nothing matters until a contract is signed and executed by both parties.

Would it not be more incentive for sellers to respond if all three knew that you were making three offers and looking for a quick response.

maly is 100% correct. Until you have a signed contract by both parties it is the wild west in terms of what could happen.

(Matthew Russell - Brown Harris Stevens)

Apt 23 has a good point, assuming they are very very comparable units.