May I ask - why are you looking to buy negative rep accounts? They're mostly used by scammers and cheaters and they command no respect from the users on the forums - why would you want to buy them?
He probably wants to use it for signature campaigns. Negative accounts usually sell for really cheap (A negative Senior probably sells for less than 0.03
BTC compared to a neutral Senior selling for ~ 0.15
BTC) but there are some campaigns that accept them and pay decent rates to negative trusted users as well.