Some folks think their dogs, and kids, are just perfect and those are the ones that could be a problem. 

After recently spending several thousand dollars renovating a rental unit to what I thought was really nice, the new tenant asked if I would be willing to replace perfectly good sliding closet doors to newer, more modern ones.

Perfectly reasonable.

@Steve Babiak  perfectly fine to sell property you own..

well it would be true you would only get 98k since 70% of 140k is 98,000 so in that case you would get the lower of 1) 70% of appraisal (as in current market value) up to your  acquisition cost (100k) OR acquisition cost as defined above.You'd get back 98k and will have 2k in the "deal," still plus your rehab of course assuming its a deal and its not in perfect condition upon acquisition.

I almost had the perfect rental but I got beat out by a CASH BUYER!  

I think something like that depends on your location, if your in Seattle that could be perfect, but if your in Indianapolis or Saint Louis, probably not so much.

The real estate market itself is not a perfect, functioning market.  

There are many reasons and it's perfectly fine to do so.

You can try to stain again/darken the floor even more so that those pet stains spots are less visible but because they absorb the stain differently you might still not have a perfectly even floor.