Once a mold inspection was performed and it was determined what type of mold is present, that's when I would give informatiion to my clients and let them decide. Some molds are quite toxic, most are not. If I was buying and the black mold (Straph...) was present, I would think long and hard. Molds can be remediated, but beyond remediation, the source must be removed or taken care of or the mold could come back.
I recently sold a house with mold. It was a pennisyllium mold which isn't toxic at the level present in the house, but had elevated levels 8X the amount outside. We got 2 estimates for remediation--one for $5400 and one for $2100! Both companies doing the same work.
Like Ute said, there are no recommended standards, no EPA acceptable level charts, basically no interpretation data out there. I have a great article about mold and the "scare" that the industry has aroused with homebuyers. If anyone would like a copy, reach out to me either through Trulia or my website, below. I'd be happy to fax it to you.