Meta Search Engines - Grouped Ads

[matthewamzn]

I'm in quite a few advertising networks. When someone does a search for my keyword on some of the popular meta search engines, my ads are at the top.

"Found on Ads by Yahoo!, LookSmart, Ask.com, MSN Search, Yahoo! Search"

Does the meta search engine take the highest bid from these networks (only charging for one click). Or am I being charged by all the networks (one click for looksmart, one click for yahoo etc.).