Hello everyone, thank you in advance for taking the time to help. A client of mine has a condo that is going to be listed for sale and after the tenant moved out we noticed 2 small dark stains. The floor is a 1/2" planked prefinished oak - stained red.

First, do you feel I could get the black stains out with out replacing the flooring? Second question would be, what is your opinion on the cause of the stains. The floor was less than a week old when the tenant moved in, brand new.

Thank you again

The stains are the result of negligence. These are probably from urine, not just water.
I hope you have a large deposit. The boards will need to be replace to remove the stain.Then the whole floor will need to be sanded, unless there is a floor joint between rooms, or you make one. The spot repair idea will look unacceptable.
You might want to leave instructions on how to care for the floor for the next tenant.
The picture shows what looks like a dried puddle.

You could very lightly sand and stain the affected areas, but it will be a noticeable repair. Even the most artistic stain guys can only do so much.

I did once have a client cut out and install a fake register to cover a stain from a leaky potted plant. The manufacturer no longer made that material so board replacements were out of the question, however, the stained boards were near enough to a wall that once we cut the spot out and dropped in a register, it looked quite natural in the room. Somewhere I have pictures, I'll post them if I can find them

Thank you for the responses - that is a good idea with the registers unfortunately the total affected area is much larger, or I would need 3 or 4 of them to cover everthing

If you do not have enough deposit to cover the"repair", you can always go to small claims. You could get a judgement, but it may be hard to collect.
Sorry.