I've had a $7K diamond sale, and since that time have sent thousands of targeted clicks to a high end jewelry merchant at LS (not Blue Nile) with no sales.
As of now, Blue Nile (at LS) will not pay affiliate commissions on sales that are under $1K if Google Checkout is used; and from my experience, there's a price point limit to the ease and frequency of getting conversions, to a high degree depending on the price of the items.
There's a price threshhold where conversions can be expected, depending on the vertical and/or the niche or product line, and either they pay commissions on ALL sales, with a decent return day and commission amount, or it's nothing more than just giving the merhant free branding. No commish on sales under a certain amount? Unreasonably short return days? No thank you.
On higher end sales, return days are critical from an affiliate point of view, and with a space that has traditionally low % of conversions, the % paid per sale can mean the difference between choosing which program to promote, and even more importantly, the return days.
Truthfully, I'd suggest Shareasale (or Avantlink, another small ethical solution), since the startup/operating costs are lower and consequently, more can be afforded with offering good commission % payout as well as longer, more attractive return days.
It isn't so much the network as what kind of inducements you're offering and what you, yourself, are doing to recruit quality affiliates.