Take an ice pick and poke around. If there is a rug your will poke through it but if the floor is good the pick should stop there. You may find areas that you FALL through and areas that are SOFT. In either case those are areas that have to be addressed.
If you find a soft spot don't stop testing at the wall or door. Rot does not stop at partitions that are above the floor.
He said a pipe problem below the floor. There should not be any pipe, other than sewer, under the floor. It is unlikely that the sewer system would fail in such a way as to cause a problem in the floor. The one exception is the point where the toilet is bolted down to the floor.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles