YouDontKnowMe - 3:08 pm on May 2, 2010 (gmt 0)
If you're being offered BIG BUCKS that you wouldn't earn otherwise from that site, then yes why not go for it?
Like suppose you have a high PR site which normally earns you only $15 per month in sales or ad revenue. And you have no idea how to better monetize it. Then someone offers you to buy a link for $100 a month. Then you would be dumb not to take the offer.
However, if your site is already earning $250 a month from other sources (AdSense, product sales, affiliate earnings, etc), and he offers you $100 for a paid link which could hurt your site, then it's not worth it.
It's always situational. Think carefully about it.