I visit and analyze the property, and estimate rehab costs (with experienced inspectors and contractors), add a buffer for unexpected repairs, and provide a financial model with an ROI comparison of a traditional rental vs. short-term rental.Any guidance/tips (positive comments only please) would be greatly appreciated!

My advIse Is purposely start to Save back rents for the repairs you know you’ll be doing in the future .

Most where value-add situations in which I was able to help with the "full picture" so to speak by giving them estimated purchase cost, value-add cost, after-repaired value, and estimated sale price. 

I "think" they are big, active, good at winning the auctions, and have big reputation.....I cant get them on the phone....but am intrigued by them....and what exactly they are...

Paint, minor repairs and necessary maintenance only.

The Profit you will have is not necessarily 2k a month what about fixes, insurance, utilities, trash, and just pesky little repairs? 

I had one recently, took me a few weeks to get it cleared up but instantly repaired my credit. 

In your shoes, post notice on the door and take a photo with your phone (timestamp proof) and also leave a message on their voicemail, indicating your intent to enter to do roof work at XX time on XX day.

After taking into account property taxes, utilities, water, insurance, and a 10% repairs & capEx fund, I figure he's making ~$5,000/month. 

If rents are $1600 and you got it at a discount, meaning they paid repairs and sold it for what they owed, you still couldn't make any money on this deal.