Paul
I wont buy or sell a single link for a site that makes me decent money these days.18 months ago was much different ,sadly i own two pr8 websites and all i can do is look at the pretty green in the tool bar hahaha.Thanks to google i have 11 pr7 sites to write off on taxes as i sold them at pr4 values 
Having said that our seo company in canada is still rolling with the punches and still did 7 digits in business in 2008 so far.SELLERS have the higher risk than buyers these days,we did one deal for a casino client and 77 of 90 websites we bought 3 links from got banned last update yet our client was not affected.
I don’t like advertising the fact i own a very popular SEO company in Canada but I’ll make this statement on record ,generally our clients have shifted at least half their budgets from links to content and ONSITE seo services.Two years ago nobody cared about the subject of the website they linked to but just the pagerank ,now finance sites will only buy from finance sites.Also i had one client who refused to pay me because there was a air pump link on the FINANCE site their link was placed on.
Final tip for people buying or selling -avoid a highly popular webmaster site as google snitches are all over there.I think i have enough proof to satisfy myself as my clients that google employees troll the forums for people buying and selling links.