Do the Dwarf Noble origin and you will find out that Bhelen is pretty much a backstabbing prick.
Spoilers for the Orzammar quest:
[hide]Also, if you bring the contracts Bhelen's guy gives you to show the supposedly doublecrossed nobles to the Shaper, the Shaper will point out that the contracts have been altered to make Harrowmont look bad. Whereas if you back Harrowmont from the beginning and enter the tournament, you'll find Bhelen's been blackmailing Harrowmont's fighters to get them to drop out.
If you tell Bhelen that Harrowmont is having you go after the crime syndicate, he has you plant faked documents in the hideout to implicate Harrowmont, whereas if you do it the other way around, Harrowmont has you search for documents in the hideout that end up implicating Bhelen.[/hide]