Documentation is the thing you can actually verify. Licensed for septic work in the county, certified disposal with paperwork, and a written report of what they found rather than a verbal all good. If a company hands you records without being asked, that's a decent proxy for how they work underground. The other tell is whether they push repeat service or fix the underlying issue; we've stayed with
rocksolidexcavationsc.com/ because they've twice told us we didn't need something. Ask about DHEC compliance directly too, it's a fair question and the answer tells you a lot. Ask for references from jobs a few years old rather than recent ones, that's where the real quality shows up.