How to negotiate with bank for mold you can't see?

[Bienes Raices]

My offer was accepted on an REO, and there was a strong smell in the house before--then the bank repainted the interior, probably to cover up the smell. I'm pretty sure it was mold, although the only visible mold I saw was a small trace of grayish stuff on the wall. I don't know for sure if mold is there but if it is it's hidden behind the drywall, or somewhere else.

To have air samples taken and tested, it's anywhere from $350 - $700, depending on the number of samples. However samples aren't going to give me proof for the bank of how much it would actually cost to remediate.

What do you do in this situation--skip the samples and just have some remediator come in there and try to give an estimate?