[crocowhile]

not quite. What OP described would not work in automated finance, where once the book approaches $5 an army of computers would try to buy it before him.

[Jd]

I'd imagine that's only so if some human has intervened and told the "actual value" of something.

However, I'd imagine that in just as many cases, if not more, there is no real "actual value" -- only computers playing with each other.