What’s my best option to argue there.

@Kamal Sukhija, The single member LLC option as been mentioned a couple of times. 

Hey @Zachary Harrison I will 1 up as they say what @Jaycee Greene has said, and that they will get a higher price with seller financing...but perhaps you make both offers anyway? 

Instead of jumping into an expensive Long Island market with negative cash flow, consider investing in a Texas market like San Antonio, Houston, or DFW suburbs—these areas offer strong rental demand, lower property taxes than NY, and better cash flow potential.

But, it may not offer the ROI as other locales, and it may not be "fun" like buying in a favorite vacation spot.2 - The highest ROI folks - Self explanatory, will go where ROI is high and/or regulation low.3 - The second home/retirement minded - These people are looking for minimal ROI but want the house in a specific location because they like to use the property and want it to pay for itself.

The Phoenix real estate market continues to evolve, offering both exciting opportunities and unique challenges for house flippers.

For a better estimation, find a business broker in your area.For the loan options, speak with your banker and try to get involved in local real estate groups.

If borrowing against stocks is an option, do they have to be stocks held within the US and/or do Canadian stock investments count as well?

I think you should also confirm to them what lease renewal terms you are offering them so they can make an informed decision.If you make the repairs, you'll create some goodwill with the tenant and they will be more likely to renew.

If a HELOC isn't an option due to Texas laws, you could consider a cash-out refinance with another property or a portfolio loan, even if you want to keep your current rate.