Charles,
A DAR is a Designated Airworthiness Representative. That is a person that has been certified by the FAA to do inspections to determine eligibility for, and issuance of, an airworthiness certificate.
This person may or may not be a good person to have complete a detailed condition/pre-buy inspection.
A better choice would be someone that has extensive experience with building the RV model you are considering, and even better would be if they are also an A&P, but not essential.