If I buy a link and the PR decreases or increases, do I get a refund/pay more or is it a one time sale? What is the convention for this?
if your buying links for the little green bar then you don't understand how to buy links. Sorry but it has to be said. Uninstall the darn toolbar please.
If the PR goes up are we also able to bill the person who purchased the link for the raise in PR? ha ha ha PR is important, but it is WAY over rated. Always think about the relevancy (and quality) of the content where you will be purchasing a link. (traffic is good too!)
I don't think most sellers would agree up front ot refund based on PR ratings. That is the risk you take when buying links. Just like if it goes up they dod not expect you to pay more for the three months you already paid for. This is a good reason to be sure who you are dealing with and check out the site well. Some people buy expired domains with high ratings , put on crap content and seel links. They know the PR will drop but they just want to make the quick buck. Do your research and check out the whois for the site. The only link buying I do is for traffic on a site relavent to my site. JMO
In PR terms buying links is a gamble similar to buying company shares -- the PR may go up or down but (within the terms of the original agreement) you won't see an decrease or increase in the price paid for the link