If you can see more than a few square feet of growth, call somebody. But visible mold is just the obvious case.
A musty smell that won't quit, especially in a bathroom, a basement, or right around your HVAC vents, usually means something is growing where you can't see it. Same goes for headaches or allergy symptoms that clear up as soon as you leave the house for a weekend. And if you've already had a test come back with high spore counts, remediation is the next move.
Mapleton gets dry summers, which fools a lot of people into thinking mold isn't a Utah problem. It absolutely is. The moisture just comes from different places here. Winter snowmelt off the Wasatch soaks into foundations. Lawn irrigation running against the house all summer keeps soil wet where you can't see it. Tight, well insulated homes trap humidity from showers and cooking with nowhere for it to go, and then condensation forms on cold basement walls in January. Finished basements are the big one in this area. A slow leak behind a wall down there can go unnoticed for months.
If you suspect it, test for it. If it's confirmed, don't sit on it. Mold spreads, and the bill grows with it.