Mold!

To prepare for a pro's visit, compile a building history. "You know," says Bishop, "the age of the building, likelihood of water damage, where leaks have been experienced lately, bathtub overflows. Consumers may think they mopped it all up, but that water may be pooled up below the floor." Leave the actual prep work for the pros. "When consumers start taking things apart, they often get into trouble," Bishop says. "Their well-meaning efforts to fix things up may result in increased cost." Pro fees range widely, says Bishop, "but any quality firm will give you a ballpark estimate. Then if they get into the project and discover that it's worse than expected, they should stop and discuss the increased price in advance."