I am curious, why would someone post bump a forum for two days only? A forum owner with a long term vision, wants continuous daily traffic over the duration of the forum's existance to attract attention from advertisers. The Google Analytics will reflect a spike and then normal traffic, so it would be of no use.
If I want to advertise on a site, I will ask for the sites performance reports over a longer period. So I would rather pay for posting over a period of a month to generate sustained traffic. You can place the payment in escrow or you can pay weekly to build trust. ^hmmmm^
Reason I don't do that is: 1) Main reason: I don't want to not have enough funds and end up getting a bad reputation. I would much rather play it safe and go day by day. 2) I do not want my forum to be a pay-to-post forum, but rather an active and quality forum