How do you find and compensate a good designer for overall material choices and color selections? 

One was because the lights had gone out on the main floor, and "it's too dark right now to go down to the basement to check the generator."

So, whatever it is... eat the same meal, listen to the same song, wear the same color, etc.

From the outside, it will look like a dark room, and from the inside, you'll have a fresh slate to install your shower surround (just make sure you don't screw through the plywood and shatter the glass behind it though!).

I have had mostly great guests, but the few that I've had that were terribly messy (much of what you describe but also smearing pizza toppings on the floor, having an easter egg hunt (I found some of the eggs) with chocolate in fabric and pink maybe egg coloring staining two sets of sheets) and yet were given 5 star reviews from prior hosts.  

I made an Excel spreadsheet and color code the ones that are higher in the red or orange colors, and low balances in green.

@Scott Mac That sage color is gorgeous!

A faux wood look with an almost black or dark grey siding would help distract the eye.But, all of this costs money, and typically beyond some cleanup and fresh paint, on a rental is the best bang for your buck.

Vibrant colors, wallpaper, etc.

having an incredible onsite manager, adding colorful flowers to perk up the curb appeal, paint the windo shutters to make them pop and renovate the interiors.