They did me a favor by stealing all the old dirty stained carpets.

If the switch is white you can just spray paint them.It depends on what kind of rental you have with what they expect.We have small old water stains from previous leaks on the ceiling when tenant moves out.I buy a spray can of Kilz for 5 bucks and usually last about for 2 of my apartment units hitting spots.You can't tell afterwords with the ceiling and it looks great.It's cheaper than scraping popcorn and trying to match or scraping the whole ceiling and a flat ceiling because it is old showing all imperfections if you just scrape and paint it.On the light switches I agree it works to replace them all but in older apartment buildings I try not to do that because what I have found is the wiring in behind is cut short or has too much excess crammed in.So if the wiring was all clean and the right slack from out of the box it would be easy to replace.I have found that some go smoothly and the others are a bit of a pain to change out making adjustments.The Kilz for the ceiling I only do that on non-active leaks where the drywall still has integrity to it and is not sagging.If it is sagging I cut out and put a patch in and then popcorn over it after priming to stick.All my tenants want is a nice,clean place to live.If you have a high end tenants paying premium bucks then finish level and what the tenant expects will change.In mine replacing everything will only net me maybe another 30 bucks a month in rent and the thousands spent will take 5 to 8 years to recover if everything goes perfectly with each unit.

A different person did the walk-through with her and didn't mention anything about the carpet needing replacing or a pet fee.They sent pictures of the underside of the carpet after they had pulled it up and there are numerous stains of various sizes.

You want cheap siding, like vinyl, or stain grade clear cedar.

The states we operate in do not like us charging the security deposit for cleaning we do ourselves, so when I walk in and it's beyond what I consider normal, I hire out to a company that charges about $100 for normal cleaning, then separates the "Excessive cleaning" on the bill, adding whatever additional time it took and why, like oven cleaning, excessive grease, extra attention in the bathrooms like dirty shower stall, toilet stain removal, etc.  

This is to avoid any issues at the end of the lease where the tenants may disagree on who broke the microwave or stained the carpet.

For my flips, if the roof shows any signs of wear at all (even staining), I always replace them.I think the answer to your question depends a lot on what you plan to do with the house and how competitively it's priced as-is.

My wife sent me a photo of the underside of the carpet he flipped, there wasn't many stains, you could see where it was shampooed for puppy accidents (a ring of the spot).

examples of things I have found and come up with: Staining cabinets and getting hardware, Deals on Crown molding on the secondary market, new light fixtures add a upgraded feel for cheap,French doors from the secondary market.  

I've had to buy bedspreads for all of my beds 3 times this summer, have had a half dozen towels get stained, an electric tea pot get melted, the furniture gets damaged, etc.