In South Carolina, the CL 100 is an important part of residential real estate transactions. The CL 100 is a test for termites and wood rot. Generally, the test is ordered and paid for by the seller. It costs about $100 and includes an inspection which identifies visible infestation and damage caused by insects, usually termites or beetles, and decay in accessible areas of a structure.
CL 100s become important to the real estate transaction because they are often required by the mortgage lender. If the property "fails" the CL 100 (ie. moisture levels are high or current/past insect damage is observed) the problem needs to be remedied and then the company offers a "clearance letter" , vouching for the moisture level and condition of the property and meeting the lender's requirements. In some cases, the mortgage lender allows the buyer to strike the CL 100 requirement from the contract, allowing the property to close without it. Be sure to talk with your realtor about this part of the process.