Nope, too much of a security issue! 

This is because Mortgage backed securities are in direct competition with investors looking for "safer" investments backed by the full faith of the United States Government. 

After  exhausting security deposit is sometimes less expensive  to give them a stipend to leave.

I explained to the seller that my offer contained a substitution of collateral clauses and I would be exchanging the note they held on the subject home with a note of similar principal and interest secured by a different property of greater appraised value.

If the property is paid in cash and later a mortgage is secured does it impact the UBIT question above ?    

I’d appreciate some feedback on my current approach and advice if any.Here’s what I’ve done so far:Pre-Approval: I’ve secured a pre-approval amount and interest rate from an online mortgage lender.Property Analysis: I’m using the mortgage and STR calculators from BiggerPockets to assess the financials for potential properties.Neighborhood Research: I’ve been exploring different neighborhoods using Niche to get insights into schools, safety, and livability.AirDNA: I’m considering subscribing to AirDNA for data on occupancy rates and rental income estimates.Questions:Is AirDNA worth the investment for STR data?

I would want my money to be secured by a promissory note and mortgage on the property in question, and thanks to the advice from some on here, if the property in question isn't enough to cover it, I would need to attach a lien to other property to ensure I can get my money back. 

Have all your ducks in a row so you can move quickly on securing the deal when you do find the right one that the numbers work on.

Security deposit amountYou can find plenty of examples by searching for "tenant estoppel certificate doc" or exchanging "doc" with "pdf" for more options.Here is an example and explanation: Sample EstoppelSome have a lot of legal jargon but this document does not need to be so detailed.

He sent me a contract which if I sign will pay him a fee of 3% of the money secured.