What is their previous rental history like?

I am assuming that you have a well documented move in inspection showing that the caulk was in good condition when they moved in?

Sometimes you get lucky.You could even bring up the subject of seller financing (search online for ideas of how to structure a seller financed offer), and make sure a competent real estate attorney helps write the offer documents (if it gets that far). 

Therefore, if you look at history, real estate has continuously performed in an upwards fashion while, like any other investment, has experienced short lived corrections from time to time.

A great REALTOR will help you gather rental history and the cost to own and show you good sites for pulling rental projections, but you will need to do your own calculations.Everyone's mileage varies.

It depends on how the transaction is structured, and the history of the title and timing. 

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

There's only about 2 types of work permit I know: closed  vs opened work permit: where the former has a condition of which employer the holder of the permit can work for (it's specified on the document); while the latter does not have that condition; hence, the holder of the open work permit can lawfully work for any employer.

However, much of our document and data collection was handled by loan analyst Taylor Vassey.

Is it a reputable company and will the documentation provided from the study hold up in an audit?