Bottom line is how much profit you make. Right above that line is how many units were sold. Whether you sold them yourself or through a partner, it's still earnings! It's *usually* advantageous to offload marketing and sales to a partner. They may do it better than you!
You have options, at different levels of involvement:
1) partner handles all aspects of all sales. That means they actually order and keep a stock of your product, and they do all handling and shipping. You sell products to them at wholesale price, in advance. aka retailer.
2) partner makes the sale, and accepts the cash. They have their own shopping cart (or store), and use you as a drop-shipper to handle product fulfilment (warehousing, shipping).
3) They do the marketing, but they pass the customer along to you to accept the cash and do all the handling and shipping. You merely keep a referral token when they pass you some traffic, and pay out a commission to the partner. aka affiliate.
No matter which relationship you have with your resellers, give them plenty of leeway & cooperation where it concerns usage of photos and marketing materials. If they want to have the info on their own domain, let them. If they want to handle the e-commerce and the marketing and the product fulfilment, let them do that too!
By being strict (greedy?) with your web content, you gain control... but you will lose sales. The more cooperation and resources you give to the partner, the more they'll sell.
If you're anxious about duplicate content and copyright, take a step back. Think of what you're gaining by hoarding your images and text, versus what you gain by letting them use your materials. Which attitude is more profitable?
I was (a few years ago) in charge of a site with a humming affiliate relationship with a manufacturer of tangible goods. We "borrowed" all their gorgeous professionally-produced product photos for use on our site, and spent oodles in marketing the products to the best of our ability. Business was excellent.
One day, we got a letter from their lawyer, asking to take all the photos down!
Instead of complying, I made a phone call to the manufacturer for a friendly chat with their rep. If we remove the photos from our site, I said, sales *will* plummet. When sales plummet, revenue drops. We were at the time their #1 reseller, representing about 25% of their total sales. After that conversation, they had no problem calling off the lawyers, giving us carte blanche with their photos, and found that with their increased cooperation we were able to increase our sales even more in the next quarter.
that's a "Win Win".
the moral of the story:
Sometimes worrying about SEO gets in the way of good business sense!