I just tell people "until you turn in a non refundable deposit, the game goes to whoever comes up with money first." Doing this for 7 years now, most of the time, I take enough pictures to pacify anyone - I tend to know th high traffic area on games I intend to sell.
If I take 30+ photos and someone still needs more (has not happened yet), I'm prepared to decline and wait for someone else. I have 25 hours worth of work in a 24 hour day. I value my free time, and I'm not wasting it taking photos of the inside of each leg or something equally silly. What I post here sells: every...single...time.