Why is it difficult to get an accurate cost for excavating when quoting my home?

If the lot is cleared or just a flat lot with no trees, quoting the excavating costs is simple.  It can become difficult to quote the excavating for a basement home when the lot is fully treed where you can’t determine the slope of the lot up front.  By not knowing how much the lot slopes, it is hard to know how much excavating will need to be done.