Forget “PR7” for a moment as that could be clouding your judgement.
If the site is being sold then you have to ask why, maybe its tricked google into getting to that meaningless figure in an an attempt to then get decent money by advertising on it/selling it to people still obsessed by visable PR.
Look at the quality of the back links and how they have got there – are they genuine or bought etc.
But even then they will only have real long term effect if they are pointed at a relevant site.
If you buy it in the hope of boosting your site, it could do damage i think – say you have a casino site which has genuine on topic casino links to it and it suddenly gets thousands of ladies shoes links – how will google think thats natural!