US credit (some lenders may require 1 or 2 credit scores to qualify you).

Alternatively, my BIL has "invested" in baseball cards.  

Any good recommendations for the collection agency or any way to get the money back from the tenant or any way to report it to the credit bureau?

I recently did one where the lender did allow it but that was because of our position as a great customer of the bank and our impeccable credit record.  

If I were in your position, I would look for a bank or credit union that will give you a line of credit against the rental property.

It will co-exist with other "new" payment methods such as google pay, apple pay and credit card etc, because the target customers are different.

Ask for a discount for prepaying for an in house credit?

They wanted $1.2M to payoff  maturing HML on a $2.5M property. their credit was 580 and we told them we would not give you a loan but we would buy the property from you for $1.2M, provide you with a 12 month lease with an option to buy. in 12 months you either buy it or its ours. 

Several options you can explore to get the down payment capital: Solo401k; HELOC on personal residence or from equity of the SFR; Cash Value Life Insurance Policy; Business Credit; Private Lenders, to name a few.

If you’re looking at retrofitting to separate heating for each unit (like furnaces or mini-splits), you might be looking at a higher upfront cost, but it can shift utility expenses to tenants and improve your NOI.I’d factor in boiler age and efficiency when analyzing deals and if it’s near the end of its life, negotiate a price reduction or a credit.