Assuming you don’t plan to owner occupy the property, buying vacant property as an investor carries risk and is quite speculative.

This was an easy decision for me as I wanted to carry on the legacy of my family in this neighborhood, and with such a short supply of deals in our market currently, it was a no-brainer for me to buy the home.

However for some reason the letter from the lender carried a lot of weight to the selling agent. 

Conventional financing through a local lender plus a seller carry back.

As @Clifford Paul had mentioned try small credit unions, they keep their loans in-house so they can carry their own underwriting criteria.

But should I carry the burden of a huge house payment for a house I don’t use?  

Why don't you try and bow out, you'll lose your deposit but at least won't have the stress of carrying 2 deals.

I have an investor that owns several lots and wants to offer Seller carry terms and subordinate his seller carry to the bank's construction loan.

That seems slightly paternalistic and carried to its logical end will mean that this forum will only be used beginners and some simplistic investors who like hearing themselves talk.I don't think that using operational cashflow as the core metric on BP is an error or a misunderstanding, I think it is a conscious choice due to it being a simple and safe metric that minimizes the likelihood of newbie investors experiencing overwhelm or major loss early in their investment careers and going back to "watching dancing with the stars".

Do you have large carrying cost, and how many months can you go etc.