This also extends the life of the carpet since rarely, in my experience, do tenants hire a professional carpet cleaner...opting instead to rent the cheap machine at the grocery store or not do it at all. 

IDK if they became stained and thrown out or the cleaners lose track of them, the mattresses have remained clean.

Overall I'd agree that cases of owners being sued and taken to the cleaners are rare, however even the threat of a case can cause stress, take up time and create expenses for an owner.

I have a check-in time after 2PM, check-out by 10AM and get regular requests to extend these times, which on occasion I try to accommodate but limit this keeping my cleaners on a regular schedule, giving them some flexibility to clean the place thoroughly. 

Any environmental concerns with any tenant, like a paint store or hobby shop, dry cleaners, pawn shop or print shop?

To manage common spaces, I suggest a) house rules b) hiring cleaners who comes by once per month so no one feels like they're being told what to do.

In all cases, they sided with me (make sure that either you or your cleaners take as many pictures of the damaged/broken piece), but the higher the price tag, the more rounds you will have to go with them, and they might not pay you back the entire amount.

And even presuming there is no ethical conflict of interest, does this sound like I'm about to get taken to the cleaners?

Lots of good posts here, one extra point to call out: Make sure you have access to cleaners, handymen, etc for the property.

Often times, these new owners will be desperate to sell their old houses ASAP.Contact mortgage companies; they may know of people wanting to sell their old house/last houseHire bird dogs (sometimes even through craigslist “help wanted” ads)Send mailers to Bankruptcy court listingsSend advertisements, business cards to Accountants and CPA Firms: They have clients with financial problems where an investor can be of help.Send ads, mailers, business cards to real estate attorneysAdvertise “We Buy Houses” using Apparel with Logos: Hats, T-Shirts, Golf Shirts,Send to anyone getting their car repossessed: If the car is going the house isn't far behind.Send ads, business cards to carpet cleaners: Many of their customers are preparing a house for sale.Send mailers to charitable groups/churches: They frequently receive gifts of real estate, but they'd rather have the cash.Send ads, business cards to City & County Inspectors: Code violations and red tags.