I think it would only be a conflict of interest of HB developed the games (which they don't). Selling vs developing. I don't see how there would be a conflict of interest.

Unless you mean, IGN having control over the games they sell because of the games they review. Though, it said HB will stay independent.

Humble Bundle will retain their independence. I'm not in the least bit worried about this.

Mergers and takeovers have not done much good in the tech\hardware and software industries in the last several years. As long as HB has a clause in the contract stating IGN keeps their fingers out of the cookie jar, like what ID Software did when they got bought out by Zenimax in order to prevent forced outside use of the ID Tech engines, this could lead to a dangerous path.

I can't see what HB can gain from this.  Would seem like a negative. Humble Bundle have been really good at offering some good deals.  Why do they need IGN?