Here are some of my suggestions
1) Treat people as if you wish to be treated the same way
2) Be Honest
3) Be on Time
4) If you make a mistake; admit it; fix it; and move on.
5) Good pts by Mr Rudd: Describe Lots honestly (Obviously a PSA 1 1933 Goudey Ruth can probably be explained with a good scan
6) Good Scans
There are more; and I'll defer to someone who can create the 10 commandments of good auction houses!
Regards
Rich