Pen and paper, spreadsheet, or whatever provides the information you need.

The previous owners took reservations mostly by phone, wrote them on a big paper wall calendar and hand keyed CC numbers into a terminal 😲The bunk beds have been a huge win. 

This is the simplest method, but it also means your tenants are more likely to abuse the utilities by leaving windows open with the heat or A/C running, leaving lights on, ignoring the toilet that constantly flushes on its own, etc.3.

Class C and D areas/properties will always cash flow better on paper, but on paper things like extra repairs, turnover, evictions and such are often not taken into account. 

Beyond that, every city I have been to has rough areas where "cash flow looks great on paper" and "nice areas where appreciation should be great".  

There is something called a "wet wall" that the pipes go through behind the toilet and sink or wherever pipes are.

Apple has been quoted a ton in papers and every realtors says it to buyers etc.

Suggested to do that earlier than later, so there is no liability on a tenant who is not on the lease paper.

Also, if it's Lennar, be prepared for problems, insulation issues and therefore paper thin walls. 

You’re not required to rent to someone just because they look great on paper, but you should ensure that your reasons for declining them are grounded in business-related concerns (e.g., concerns over rental history or ability to care for the property, if documented).A good practice is to follow a consistent screening process for all applicants.