Oh tell me about this.
You want to sell something, THEN SELL IT!.
Humans have limited time on this here Earth and will make split second snap judgements subconsciously, this includes sales.
SH*T photos do not sell your gun or what ever well or you'll get low ball offers at best.
Photos that are
Dark
Poorly exposed
Flash glare
Grainy
Blurry
Too much background distraction (think horrific bed sheets)
Too much Dutch angles
Part of the product your selling has been cropped out or framed poorly
No sense of scale
upside down photos
Dogs/Cats/people/body parts in the shot
Dirty/unclean background - If you treat your living space that badly, how badly did you treat this product
For me though the biggest faux pas and cause of me turning away from a sale
FEET
How hard is it to not get your feet shot in the image?
Wouldn't be so bad if it was a pair of trainers or shoes, i get put off by normal feet and sometimes you see some proper grubby toes.