In my experience.... if a customer is going to use a cashback or vouchercode site - they're going to use it regardless of the merchant or product they're looking for.
If a merchant is to put their foot down and say "
NO" to voucher code sites for example...then its fairly likely that they're passing up a good chunk of business (unless they're the only merchant in the UK selling a certain type of product... which doesn't happen all that often - there is so much competition out there!) ...and who want to lose sales to the competition?!
I can't agree with your view of the voucher code sites... being lazy?!... keeping up with all the various offers and codes and updates must be pretty knackering. Writing content is one thing (and I've done this myself) .... but at least once its written, you're finished to a certain extent - the voucher updates are never-ending!
I understand why you're frustrated about losing commissions (although... do you have a good way to put a number on what you're losing?... its easy to assume you're losing sales to these guys... but do you know for sure? Maybe Hitwise could shed some light on your downstream traffic so you can quantify the damage?...just a suggestion)
Why aren't you spending your time adding the voucher codes to your own sites? Your post must have taken a fair while to write, and due to the negativity - it hasn't provoked the best responce so far ...its got to be said
Anyway - my point is that the majority of codes are open to anyone to use.... so if a customer comes to your site and see's the content, and the discount all in one place - why bother looking elsewhere? (it would at least improve your chances)....fair enough there are exclcusive codes out there in the market... but often the codes offer only a marginally better offer than the standard codes - so you should still get some conversion from those of us lazy enough not to shop around too much ...me included

)
Just a few thoughts anyway - feel free to shoot me down if you like, but I can't honestly see a massive amount of clients stepping away from cashbacks and voucher code sites any time soon....bottom line is, customers are becomming more savvy, many are realising (with the help of the media) that they can save money and even make some money back on their online shopping.... so of course they're going to take advantage.
My advice would be to build up a base of customers loyal to your sites based on the original content...and offer the the discounts you can gain access to - there should be plenty.
Cheers
Sean