We are renting a house from a private party.

I have been on all sides of construction, so that part is where I am most knowledgeable.The appeal of cash flowing from a rental is nice.

This is a professional forum.  

I don't believe either is very accurate for a real estate professional.

Once an offer is signed in massachusetts by both parties it is considered an enforceable contract.This serves as better proof the seller actually was delivered the offer and read through it.

Contract is not bidding until both parties sign AND IT IS DELIVERED!

Heck, you're not even a party to the lease option agreement between the seller and the buyer after you assign, unless you structure a sandwich lease option instead of assigning).

but that would be a cheap shot from him and a waste of his professional time.

If landlording has become a chore for them they might be willing to do a deal with you that is favorable for all parties.

This is not the same process as a SFR purchase, where the buyer obtains a letter of qualification from a dubious mortgage broker; this is a very intensive evaluation.That being said, nothing is to stop any interested party, qualified or not from making an unsolicited offer.