In my experience, and the experience of hundreds of professional property managers I network with, counting the late fee as "extra income" will come back to bite you.

If converting a commercial unit to residential costs $50k and only brings in a few hundred dollars more in rent, it might not be worth it.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

They are people who have invested hundreds of thousands of dollars into buying units.

(full disclosure-I knew the guy, or know him, he's not dead just gone from the auctions and haven't talked to him in a few years, but he was always nice to me and I don't have a clue as to the validity of the federal charges against him, but he always treated me decently and I've got nothing bad to say about him and I know other landlords who've been demonized and slurred as slumlords when I think they simply bit off more than they can chew, while other real slumlords seem to operate for years, as long as they don't get too big) He used to kind of dominate those auctions and maybe that was a good thing, as I'm sure there's a whole cast of characters who've filed that void.Thing is, ANY property under $100k, maybe even under $150k or $200k will certainly have multiple bidders, there are a LOT of people like me when I'm looking, who have the subscription to the sheriff's sales info reports from the Daily Reporter ($600/year and you get the results emailed to you in an Excel spreadsheet on Tues, next weeks auctions emailed on Thurs) and another good indicator is I'm on an email list for one of the firms (actually out of Chicago) which handles a tiny, tiny fraction of the cases and I've looked at the "cc list" or whatever you'd call it if ALL the addresses that email is sent to and there are HUNDREDS of them on there and this is for I think Johnson Blumberg, who many weeks don't even have any cases in MKE or Waukesha Cty.

It's often because people don't want to do the research or work necessary to get prepared to invest so they do things like talk about LLCs, scaling, and look online at hundreds of properties before ever seeing one in real life.The antidote is to go to real estate investing meetups, as many as you can, and never miss.

I'm not saying you're not legit, but I seen hundreds of these very posts over the years and all the red flags are there that this is merely another guru trying to his name out by using a fake account to post a fake testimonial. 

However, I see hundreds of properties listed on Airbnb that do not follow the rules. 

One of their hundreds of clients gets picked for audit...and then maybe another...and then maybe all of them.

However, if you want honest and professional opinions from hundreds of years of collective working knowledge,  than this is the place.