Just like other search networks, they have a ton of different publishers showing your ads. It's up to you to track everything and block the garbage sources (You need to ask to have subid blocking enabled. It's a hidden feature). But, once you finally have a super optimized campaign, it's still kind of disappointing since the traffic volume is so low.
THIS^
Treat a 7S campaign like you would an adwords campaign. Use exact match, get subID/referrer blocking enabled (and track that shit), get dayparting enabled, use the MakeTop tool, test their ClickFree (domain/type-in) traffic, split test your landing page, split test your ad copy, etc. etc. etc.
Throwing $25 into a single effort, one offer campaign isn't a test. It's just as bad as throwing $25 into a slot machine then walking out declaring "Vegas Sucks!"
Build a campaign the right way and 7S can be very effective for many niches. But if you don't track and don't optimize (just like you would in BING or Adwords), you will waste your money and time.
Also understand that MOST of the traffic is publisher traffic. Everything from RSS to dead domain to in-context ads to mobile ads to actual third-tier search engine results. Watch those subIDs closely. I ususally give a subID 10 clicks per keyword (or 30 clicks total on all keywords) to convert before I ban them. If you send traffic to your own domain and have Google Analytics, you can see the referring URLs.
Also, placement on 7Search is CRUCIAL. I find some keywords convert best at first position, and some at 3rd. I assume it just depends on the inventory available for that keyword. For example, a high-traffic or high-cost keyword will probably get contextual impressions for positions 1 and 2 only, meaning the 3rd position is a safe place to bid for that keyword. It takes some testing to figure out what keywords work best in what spots.
And finally, watch those IPs. If you see a lot of clicks coming in from same IPs then BAN those subs immediately and report the IPs and click data to your rep immediately for a credit.
7Search can be very profitable source of traffic if you aren't lazy.
DISCLAIMER: I'm an affiliate. Apparently a decent one if I figured this out. I have no relation to 7Search at all.