Once you have a shortlist, sign up for an account with each one and test them extensively to see how they function.

Be patient. these are mid-term plays, so you must be prepared to go without the cash for several years.

My plumber went and discovered tush wipes sitting ON the toilet tank while trying to test the toilet.

lol I was not prepared for that.

The second piece is whether or not you pass the Material Participation Tests found in IRC 469 and the third piece is whether your participation rises to the level of Substantial Services (think hotel, B&B).4) My CPA Says I can't deduct a loss that was generated! 

There are seven tests, however the most relevant tests for STR investors include:Perform substantially all the work related to the activity.Participate over 500 hours during the tax year.Participate over 100 hours during the tax year and no one else participated more.If your property meets one of the exceptions above AND you meet one of the above tests, you can qualify to treat your rental activity as non-passive.

Quote from @Evan Polaski: @Enrique Roth, every investor should be preparing a full appraisal package.In mine, I include 1. before and after photos, 2. 5-6 comps that I want the appraiser to use, WITH explanations of what the comps have or don't have compared to mine.  

Ironically most investors don't slow down to ask themselves that simple question but will prepare a multi tab excel spreadsheet justifying the reason behind purchasing the low barrier home that lacks fundamentals because it meets the 1% rule or is a good BRRRR candidate because that's what they are taught.

Tenants told me seller had tried to sell to investors before but after meth test came back positive they were going to drop the price significantly. 

Come prepared, ask better questions, and you will get better answers.