Most disappointments here are not about condition. They are about which edition, and which volumes.
Writing "near complete"
It is not information. Say which volumes are present and which are missing, by number.
Not showing the publication page
Publisher, imprint, language and printing are all on it. Five seconds on camera answers most of a buyer's questions.
Selling an unofficial printing as official
Unofficial printings exist in this category. Describing one honestly is a sale; describing it as official is a counterfeit problem. Counterfeits policy.
Comparing an omnibus to singles
Different items, different prices. Say which you have.
Not mentioning missing dust jackets
Where an edition had them, their absence is a real deduction.
Packing a stack that can shift
Books that slide grind against each other and bruise spines. Board, bag, snug box, spines alternated. Packing manga.
Storing in sunlight
Spines fade, and a faded run is a lower-value run.
The one that costs most
Selling a run with a gap without saying so. The missing volumes are frequently the expensive ones, and a buyer who finds a gap has a real grievance.
Questions people ask
Should I split a complete run?
Usually not. Completeness is most of what a run is worth.
Are reading copies worth listing?
Yes, at reading-copy prices.
Do figures sell with books?
Separately usually, and the box matters. Selling toys.