I use all white towels and linens now as the dark towels fade and bedding discolors and look pretty lousy after heavy usage. 

If you're flipping, mold was disclosed, joists or whatever is discolored (still scary to a laymen), then painting it with Kilz will reduce buyers' fear.Rick

On another rental of mine the tub was yellow and discolored,  I spend about 50 bucks at the hardware store and resurfaced it myself.

Is that actually mold on the liner or discoloration from iron and calcium in the water? 

The old tenants used used hair dye that stained the tub, when they left they were able to scrub off the dye but now there is a section of the tub- where about 18" x 8" of the tub enamel has been scrubbed off and is discolored and rough.

After removing any hyphal discoloration, allow them to properly dry and then treat the walls with Kilz or Fosters brand antimicrobial paint.

The other students all thought the tub had discolored because the finish had failed. 

We have some real leather recliners and found that a high powered sunscreen/bug repellent seems to discolor the leather.

If the concrete does discolor, pressure washing and certain cleaning chemicals will remove most stains.I like Jack Bobeck comment about a 7-day right to cure.

Some of them were discolored.