Some just have deep pockets, they buy
their own product (through their own
affiliate links) to jump start the program.
They are able to do this because clickbank
allow vendors to lower/raise the price of their
products.
These vendors lower their products to something
like $3, they spend like $300 in one hour and
that will make it popular on the marketplace.
Other people have thousands of indexed
cloaker pages. When they submit their new
product to clickbank they redirect the traffic
from those pages to their clickbank landing
page.