“We found a house we like, but it had a major mold problem. The seller says it’s all been taken care of. Do you think it’s safe to buy it?”
There’s benign mold, and there’s “toxic mold,” so I assume you’re talking about the latter.
Many people can live in a home even with toxic mold without it ever being a problem. But mold can cause some people to develop or exacerbate health problems.
You should be okay if the seller had the mold professionally remediated (removed) and tested to be sure the mold is gone. So ask for proof of the remediation and the testing.
You could still be fine even if the seller just tore out the affected areas, but you won’t know for a high level of certainty unless it was done professionally.
Please consult a mold professional.