What is the link: in google?

So I am planning to buy a website, it seems good. I verified the income, etc -- all seems good.

For its main keyword, I googled it - and I see it in the first page. That's good.

But, one problem is:

When i search for:

link:URL
and link:www.URL
I do not see any results! This is a PR 4 website, and 44-45 inbound links.

What does this mean? How careful should I be about this? I am spending about $800, so I really want to be sure.

Please let me know your advice guys!

Thanks

And oh, he said he used a lot of posts on BMR and wiki links, that's why it has such a high PR. What do you guys think?