I have used in the past pricenoia.com, it had similar features: Amazon price history, comparison between local Amazon sites and mail notification when price reaches some threshold. I've just checked, and it looks like it has been closed in September :( http://pricenoia.tumblr.com/post/96524879555/pricenoia-shuts...
While it's true that they might have the incentive to do this because of affiliate fees, they'd need access to the particular site's price-steering specifics, which I doubt they'd give out due to competitive reasons. (For Amazon itself, the OP article doesn't mention price-steering, and the incident from 2000 it linked [1] quotes CEO who promised to never do it again)
If they don't have access to that, they can't price-steer or else users would notice discrepancies between the listed price and the site's price and the main users of those sites are the price-minded.
Yeah, as far as I know, most price-steering that people see on Amazon is actually vendor-steering. If you have Prime, they will tend to give you Prime sellers if the overall cost is less. If you sign out, it may give you 3rd parties who charge less, but have higher shipping.
That's a great point, but I think multiple approaches could be possible. For example, manipulating historical data to make the current price point attractive. That would be difficult for the user to verify.
Wow that sure would be insidious and hard to notice. I guess at the end of the day it comes down to whether you trust the site enough and what they could stand to gain from it.
For instance, Artificial intelligence a modern approach is $135 right now, but using this site I can see that it was <$90 in January of this year and it hit $100 in September: http://camelcamelcamel.com/Artificial-Intelligence-Modern-Ap...
Same story with Introduction to Algorithms, except it is now $80 and the lowest it hit was $44 in October: http://camelcamelcamel.com/Introduction-Algorithms-Edition-T...