It makes your building worth less, it makes it harder to sell, and it makes it harder to rent.No, RUBS aren't illegal in your area, but the fact that they are illegal in many areas proves it is a bad idea.

This is something tangible that you can give to other investors/ lenders to prove track record. 

Market Analytics: Use data analytics tools to study market trends, price forecasts, and neighborhood demographics.

If I buy a property for short term rental and do a cost segregation study to speed up depreciation, can I later decide to convert to a primary residence?

Study the PPM and offering materials....see how the projections meet the actual numbers and what went right or wrong. 

I learned almost all of my techniques for DD studying those memos.

A cost segregation study was performed on this residential condo in Jupiter, FL purchased in 2022 with a depreciable cost basis of $672,870.

They now say that we need to do technical analysis to prove water is coming from their unit and not from any other unit. 

Your losses even depend on number of things like the basis of your earlier property, any additional capex required like HVAC or major repairs, output of cost segregation studies, etc.

Without studying.