I know some sellers do it a different way, but I leave Feedback for buyers as soon as they pay. This leaves me in the opposite quandary where many buyers don't leave feedback. As for your question on whether non-100% feedback deters selling/buying, I definitely take a closer look at feedback...
Walt Dropo - July 14-15, 1952: 14th - 5-5, 15th Doubleheader - Gm 1 - 4-4, Gm 2 - 4-5 (hits in first 3 at bats for 12 consecutive plate appearances w/ hits). Impressive 2 days, but going by the rules, even a decent back-to-back.
Think the only thing that saved the seller was he had put up some other rare cards and had some people check his other items. The 1997 Precious Metals he had sold well too. Never knew of the 1996 Diamond Club w/ actual diamonds.