I use something similar, Invisible Hand. <a href="http://www.getinvisiblehand.com/" rel="nofollow">http://www.getinvisiblehand.com/</a><p>I haven't had a chance to check out Buy Happy yet, but it seems to me that displaying competing prices on product pages rather than when adding to cart might be a better experience. I use price as one of the deciding factors on whether to buy, and there have been a few times where the lower price that Invisible Hand found convinced me to actually buy a product.<p>Perhaps both approaches are useful.
I haven't checked the source code of the plugin, but I wonder if they add affiliate links when they link to the other prices that are lower? If they don't, I don't see why not, it seems like a nice & easy way to skim off the top of those transactions for providing a nice extension. I'll definitely try this out for a bit and gauge how good it works.
Just for reference,<p>At the moment, the best price we've found on this product is on Best Buy. If you add it to your cart and view your cart, you should see a best price confirmation.<p><a href="http://www.bestbuy.com/site/radar-laser-detector/1470022.p?id=1219052238508&skuId=1470022&st=laser%20detector&cp=1&lp=1" rel="nofollow">http://www.bestbuy.com/site/radar-laser-detector/1470022.p?i...</a><p>You only see a confirmation if we could find a match. Otherwise, we stay out of your way.<p>This Blu-ray player is cheaper elsewhere:<p><a href="http://www.bestbuy.com/site/Sony+-+Smart+Blu-ray+Player/7829257.p?skuId=7829257&productCategoryId=abcat0102003&id=1218861012727" rel="nofollow">http://www.bestbuy.com/site/Sony+-+Smart+Blu-ray+Player/7829...</a><p>Add it to your cart and go to your cart and you'll see a better offer.
Looks very nice!<p>Our Zinc Save [0] extension takes a slightly different approach. We add a button on at checkout that guarantees a fixed, better price. If you use it, we then do the price shopping for you and place the order on your behalf. If we don't get the price we promised, we keep or eat the difference.<p>[0] zincsave.com
FYI OP, I had to remove the extension because it caused other extensions to break.<p>I get this error code in the console when the extension is turned on:<p><i>Denying load of chrome-extension://amplgponnfkfhnbgojhehcaaiocgmpam/jquery.min.map. Resources must be listed in the web_accessible_resources manifest key in order to be loaded by pages outside the extension.</i><p>(I'm using Chrome Version 33.0.1750.146)
Nicely done.<p>If you're not in the US, you can give a try to our extension Shoptimate [0]. It does not compare in your cart but at the product page.<p>[0] <a href="http://www.shoptimate.com" rel="nofollow">http://www.shoptimate.com</a>