My question is about the use of the Past Perfect Simple in the following excerpt:
Back in 1995, when Bezos was shipping books from his garage, Pierre Omidyar, a software programmer, started coding a simple Web site he called AuctionWeb. Omidyar was curious if people would use the Internet to bid on each other's used items. Looking around for something to sell, Omidyar picked up a broken laser pointer. Within a day, it had sold for $14.83. Omidyar e-mailed the buyer to make sure the guy knew it was broken.
I can't find any rule that would justify the use of the Past Perfect Simple here. A friend of mine who's a native speaker of English says he would also choose the Past Perfect Simple over Past Simple here, but he can't say why.
1) What I think is that "Within a day" works here in the same way as "by" would. In other words "Within a day" means the same as "By the end of the day" / "By the time the day ended". Is this correct?
2) If „Within a day” justifies the use of the Past Perfect Simple, would it work for the Future Perfect Simple too? For example, would it be correct to say “The printer will have sold within a day”?
3) Would it be OK to use the Past Simple (Within a day, it sold for $14.83.)? What would the difference be in meaning then? I assume it would be fine, but the Past Perfect Simple works here better as it allows you to put more emphasis on completion. Similarly, the Present Perfect Simple is used to put emphasis on completion in the first conditional. Correct?