@Jimmy SamaiYou can also try bleaching the subfloor underneath and priming it as well.

Keep your condensation pumps in good working order (occasionally pour in a SMALL amount of bleach or other agent to kill algae , make sure outside tube not blocked / clogged/ kinked / frozen )

However, If a piece of baseboard had a small amount of surface black mold, it wouldn't be unusual for a repairman to clean it, bleach it, and keep it. 

These are some of the best deals I ever come across because most people don’t even want to step in the house and it doesn’t cost more than a grand to get the whole place emptied out, exterminated and bleached top to bottom.

Bleach kills some extremely high % of mold spores, but sometimes from a public perception standpoint people paint over with a primer, etc - kind of weird they just did it across the board, though, instead of targeting areas that needed it.

I had my kids scrub the garage floors with bleach and push brooms.

@Gerardo EscutiaI would check the condensation drain to make sure it is draining properly if nor add some bleach into the tubing at the return.

Here's what we ALREADY DID:1. 2 hardwood floors, resanded, then before the 3 coats of poly were added, I brought in a backpack sprayer with bleach water.

He found multiple bottles of bleach and mold cleaner in a bucket in the basement as well.

If it was bleached, left to sit overnight and scrubbed again and they wouldn't come out, that is a tenant issue due to being a nasty person.