Specifically, I am looking at partnering with an individual who owns securities (stock and mutual funds) having them take out a line of credit against their portfolio (SBLOC) at a low interest rate, and using that to purchase properties rather than using a mortgage.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Sellers may struggle to mentally shift from "owner" to "tenant," which can create challenges with boundaries and property care.Security Deposit:If you’re doing a temporary leaseback, be sure to collect a substantial security deposit to cover potential damages and ensure they vacate on time.

But somebody could use a credit card fund the immediate need and then pay it back with the policy loan fairly quickly.

Your name and credit would stay with the existing note, which you would keep paying on - ideally yourself with money you receive from the "buyer", because if they don't pay your credit is wrecked and your house is in foreclosure.If you search on here you'll see everyone and their brother looking to do Subto and it's a nightmare unless the buyer has the funds to pay the note off if/when the original lender figures out you don't occupy the property any more and are attempting to do what you want to do, since most loans are going to specify that performance.  

If comps for a 3 unit property are in the 950k range, then that is what it will come in at.The revenue from the STR will have no bearing on the value of the property itself.People argue about it from time to time, but I spoke with 10 different lenders, banks, credit unions, private lenders, etc etc and they all said the same thing.

DSCR loans are based off of down payment, credit score and either actual or market rents so it helps to supercharge an investor's real estate goals and net worth.

Leverage Local ResourcesEconomic Development Grants: Check with your city or county for grants or incentives aimed at affordable housing or community improvement projects.Local Banks or Credit Unions: They may be more flexible than larger financial institutions, especially if your project aligns with community needs.Partnership with Nonprofits: Collaborate with organizations interested in affordable housing or sustainable living.4.

I don't take credit cards but I believe stripe does.   

DSCR loans go up to 80% of the purchase price and depending on the Debt Service Coverage Ratio and your credit score you can expect rates on a 30 yr loan ranging from High 6%- Mid 8%.